"How To" use a multimeter. [Archive] - FSB Forums

: "How To" use a multimeter.


Bronco Rob
01-19-2008, 04:32 AM
This is a very basic "how to" use a multimeter to check circuits

A multimeter is a very cheap (can find them for under $15) and useful tool to have in your toolbox. A test light is cheaper, but it won't give you as much information, Test lights usually only indicate Voltage only.

Even with the cheap ones you can still manage to get data to figure out what is happening in a circuit in your vehicle.

The circuit i drew, is a very basic circuit, so please don't get into detail with it, it's to be used for example purposes only.

Some basic things you need to know.

1. Ohm's Law: V=I*R

V= Voltage (volts, we work with 12 volt systems)

I= Current (Amps, amp draw)

R= Resistance (the resistance, or voltage/current loss in a circuit)

Why is this important?

If you can get two out of the three, you can figure out the third by simply manipulating the data. V=I*R can be manipulated to find Resistance easily. R=V/I and can be manipulated to find Current I= V/R.

2. Be VERY careful when working around power sources:

A current blast as little as .5 Amps can throw off the rhythm of your heart, it won't affect you right away, but it gets very painful, and can kill you.

While it's uncommon to be electrocuted while working on a vehicle, it is VERY. VERY possible. Alternators and other components can kick out some very high voltages and amperages. So just be careful!

So let's get started:

This is your basic multimeter:

http://www.supermotors.net/getfile/601700/fullsize/pm51.jpg

We're going to be using this one:

http://www.supermotors.net/getfile/601704/fullsize/meter2.gif

For an example.

To test Voltage (V) and resistance (Ω) (that's the omega symbol, how resistance is measured), you are going to want to plug your Red Lead into the V Ω mA slot and the Black Lead into the COM slot.

That little lightning bolt indicates that the leads are fused at this point, if you start pulling in a ton of voltage, the system fuse will pop. This specific Multimeters read up to 750 Volts, anything above that and it will blow the fuse to protect the meter.

Testing Source Voltage:

Anytime you have a component that won't work, you're going to want to test it's source voltage, to ensure that you have source power. The source power in this case is the battery. This is where we will test Source Voltage.

It's rather simple.

Set the Multimeter (as seen above) to 20 Volts DC (DC is indicated by a straight line, with a dashed or dotted line beneath it). 20 VDC doesn't mean we have to test 20 volts, it's "up to" 20 Volts, and is usually the application for automobiles (in most cases there are components that have an output of more than 20VDC on a vehicle, but if you know what they are, you already know how to use a multimeter)

Now, take the Red Lead and put it against the Positive post of the battery, and take the Black Lead and put it against the Negative post of the battery.

This is a diagram of testing Source Voltage:

http://www.supermotors.net/getfile/601701/fullsize/srcvlt.jpg

Now when testing your battery, it's going to read a little weird.

A battery says it's 12 VDC. But here's the deal, it will usually test from 11.5 VDC to 12.5 VDC depending on the age of your battery, without the motor running

With the motor running it should read 12.5 VDC to 14.5 VDC. In order to charge a battery back to 12 volts, while under a load, you have to run a little more voltage to it. If you're reading within 2.5+ volts of 12, you're fine, you're not overcharging.

If you're reading more than 15 VDC, your alternator may be overcharging your battery!

If you're reading 12 VDC, you're alternator isn't charging your battery, it's basically maintaining your battery.

If you're reading less than 12 VDC, you've got an issue with your source voltage and your alternator, or battery.

Okay now that we've broken you in, on how to test voltage, we're going to want to move on to something a little harder.

The nice thing about vehicles is, that the body is grounded to the frame, the frame is grounded to the battery. The Black Lead can be put to any steel surface and it's considered a ground, you can take the Red Lead and test prior to a fuse or component, and after a fuse or component, as seen here:

Testing for voltage prior to the fuse:

http://www.supermotors.net/getfile/601706/fullsize/tstvlt1.jpg

Testing for voltage after a fuse:

http://www.supermotors.net/getfile/601705/fullsize/testvlt2.jpg

Before and after a fuse, should read source voltage!

Lets get on to testing resistance, or Ω (Ohm's):

When testing something like a positive battery cable, it's best to remove the battery cable from the source and the destination to test resistance. Components and sources can have a resistance of their own, that will throw off the reading of your multimeter.

So lets say you've removed your Positive battery cable, how do you test it for Resistance (or continuity, depending on who you are).

Back to the multimeter:

http://www.supermotors.net/getfile/601704/fullsize/meter2.gif

Move the dial to the symbol of a little circle with soundwaves coming off of it. For this purpose, you're testing for Total Resistance of 0. You expect to have Zero resistance. You don't want any Resistance between source power and the destination (like your starter).

Test your meter. Take the Black Lead and touch it to the Red Lead, the meter should now beep, and the digital reading should scroll down to 0.0000. There should be no resistance in your meter!

So you've got the multimeter set right. Take the Black Lead, place it on one end of the cable, take the Red Lead, and place it on the other end of the cable.

When testing for resistance (0Ω), polarity doesn't make a difference. Resistance doesn't travel in any direction, it's just testing to ensure the path is clear.

The meter should now start to squeal. If it doesn't squeal, you have resistance in the positive battery cable. Resistance in battery cables will cause problems, the path is not clear, the voltage and current is constricted when traveling and it's not all making it to the component.

Testing resistance in your wiring through out your vehicle is pretty much the same concept.

You cannot test the resistance of a component and get a clear indication of what it means. Different components (like a blower motor) are going to have different resistance, depending on the component. What you can do is read the resistance in the wire to and from the component.

Do not try to read resistance from the (+) positive side of component, to ground (-). Test after the component, to ground. The component will give you a faulty reading.

When testing a fuse, remove it from the holder and test it as a single entity. A fuse should make your meter squeal and the digital reading should be 0.0000. The reason you want to test a fuse as a separate entity is because a fuse can actually blow, and re-solder itself shut. This will create resistance, removing it from the holder gives you the ability to physically look at the fuse. If it looks like it soldered itself shut again, replace the fuse! They're CHEAP!

http://www.supermotors.net/getfile/601699/fullsize/fuse.jpg

If you test a conductor, like copper wire or a fuse:

And your meter doesn't do anything, doesn't squeal, the digital display doesn't move, you have an open in your wiring. The reading is called an "infinite" reading, Ω is infinite, total resistance, current and voltage will not travel through infinite Ω. This means that the fuse is blown, or somewhere between point A and point B, the wire is broken or not connected. At this point, trace the wiring back to find the open.

If you test a conductor, to ground, prior to the component:

And your meter squeals and the digital meter indicates you have a short. This means somewhere your (+) is grounding out to the body, frame, or negative wire of the circuit. With the power on, you'll probably blow fuses if this is happening.

Testing amp draw or Current (I):

In order to test amp draw or current, you need to break open the circuit.

There really isn't a reason to do this for the backyard mechanic. If you're blowing fuses your drawing too much current.

But just in case you wanted to know (THIS IS FOR DC CIRCUITS ONLY):

http://www.supermotors.net/getfile/601704/fullsize/meter2.gif

Remove the Red Lead and place it into the 10ADC slot, turn the dial to 200 A selection.

You would have to break the circuit, and actually let the current and voltage run through your meter as so:

http://www.supermotors.net/getfile/601697/fullsize/amp.jpg

These:

http://www.supermotors.net/getfile/601698/fullsize/cm6x.jpg

are a very good thing to have when testing Current or Amp draw, you NEVER want to HOLD leads in place when breaking open a circuit and running current and voltage through it.

Some tips:

~When adding a new circuit, such as lights. Always, always, always FUSE the positive feed to the lights or component. It's much cheaper to replace a fuse rather than the component completely.

~When doing something like testing your rear window switch wiring, don't test THROUGH the switch, check the switch independently of the wiring, you can get false readings when testing multiple components and conductors.

~ALWAYS, show great caution and appreciation for electricity of any sort. The instant you start taking it for granted is when it will bite you.

~DON'T be a ground. Wear rubber souled shoes and don't touch one hand to the positive end of a circuit and touch steel with the other hand, you become insta-ground, and like i said earlier, something as little as .5 Amps can throw off the rhythm of your heart, it may not kill you, but it will fawk you up for a little while.

~NOT ALL MULTIMETERS are the same, some of them have different limitations and settings, this is a basic multimeter use thread.

Once again and in conclusion:

This is a VERY basic tutorial on how to use a multimeter when testing your truck. Some of this is my opinion, not everyone may do it this way, it's the way i do it. If you see any blatant mistakes, please let me know so i can correct them. I've been up a little too long.

A Multimeter and a test light are two very important tools that you can use to make sure that your electrical system is running properly.

miesk5
01-19-2008, 10:18 AM
thanks! good to see test equipt. (and tool use) addressed!
btw, here is what Ford says about testing (TPS); Throttle Position Sensor (TPS) Function & Diagnosis TSB 94-26-4 by Ford for 93-95 (http://home.comcast.net/~miesk5/technical_service_bulletins.htm#technical_service_ bulletins.htm)

(one thAng, upper case is by Ford in the SB, not me)
"...CAUTION:
MANY VOLTMETERS WILL AUTOMATICALLY CHANGE RANGES WHEN MEASURING TPS OUTPUT FROM IDLE TO WOT. WHEN A VOLTMETER IS USED TO MEASURE TPS OUTPUT FROM IDLE TO WOT, THE METER SCALES OR CHANGES RANGES AUTOMATICALLY. THERE MAY BE AN ERRONEOUS METER DISPLAY UNTIL THE VOLTMETER HAS LOCKED TO THE APPROPRIATE VOLTAGE READING. THE ERRONEOUS METER DISPLAY DOES NOT REPRESENT A DEFECTIVE TPS.
NOTE: IT IS RECOMMENDED THAT THE "RANGE LOCK" FEATURE ON MANY METERS BE SET FOR CHECKING TPS VOLTAGE.
Use the 0.00 range to measure TPS voltage.
If your voltmeter does not change ranges automatically and the meter is set to millivolt scale when reading full range voltages, the meter display may not indicate a valid value. This can be misinterpreted as an open circuit or suspect TPS. Ensure the meter is set to volts for measuring full range voltage levels..."

Bronco Rob
01-19-2008, 01:06 PM
thanks! good to see test equipt. (and tool use) addressed!
btw, here is what Ford says about testing (TPS); Throttle Position Sensor (TPS) Function & Diagnosis TSB 94-26-4 by Ford for 93-95 (http://home.comcast.net/~miesk5/technical_service_bulletins.htm#technical_service_ bulletins.htm)

(one thAng, upper case is by Ford in the SB, not me)
"...CAUTION:
MANY VOLTMETERS WILL AUTOMATICALLY CHANGE RANGES WHEN MEASURING TPS OUTPUT FROM IDLE TO WOT. WHEN A VOLTMETER IS USED TO MEASURE TPS OUTPUT FROM IDLE TO WOT, THE METER SCALES OR CHANGES RANGES AUTOMATICALLY. THERE MAY BE AN ERRONEOUS METER DISPLAY UNTIL THE VOLTMETER HAS LOCKED TO THE APPROPRIATE VOLTAGE READING. THE ERRONEOUS METER DISPLAY DOES NOT REPRESENT A DEFECTIVE TPS.
NOTE: IT IS RECOMMENDED THAT THE "RANGE LOCK" FEATURE ON MANY METERS BE SET FOR CHECKING TPS VOLTAGE.
Use the 0.00 range to measure TPS voltage.
If your voltmeter does not change ranges automatically and the meter is set to millivolt scale when reading full range voltages, the meter display may not indicate a valid value. This can be misinterpreted as an open circuit or suspect TPS. Ensure the meter is set to volts for measuring full range voltage levels..."

I *think* there is actually a meter made specifically for automotive use. a lower end meter won't have range lock. If you were to actually go outside of 20 Volts, the digital display would read "OL" Overload.

TPS Voltage isn't going to be a constant voltage, it's going to increase and decrease depending on where the throttle is at. I didn't get into stuff like that. But there are components in our car, that will read 0.5volts and increase to 10-12 volts. There are fewer components that actually exceed 12 volts, but they are there. "OL" will let you know when you exceed the range you're in.

If you set it to read ACV and try to read DCV you'll get some really weird readings, double check your selector switch.

Multimeters come in useful in other household applications too. Any electronic device (TV, DVD Player, Blue-Ray Player, Computer) normally has a power supply that does two things. 1. Converts AC to DC power and 2. Regulates 12 volt to ensure that every component has required voltage.

It's really a useful tool to have around the house in general

95thebroncoman351
01-19-2008, 01:19 PM
and remember kids: source voltage is all most all ways 5V and not to use the multimeter on your cars computer circuits.:rockon


and props on an awsome write up rob:thumbup

Bronco Rob
01-19-2008, 01:44 PM
Wow, I'm glad I'm not the only one who's not comfortable using one of these things, great write up. I'm printing this and puitting it with the meter.

:thumbup

That's the easiest way to get to know these tools.

Turn it to the resistance setting, walk around your house and find conductors.

Turn it to 200 Volts AC and check your house electrical.

Just play with it, they really aren't all that intense or hard to use, don't be afraid of them.

Joes93Bronco
01-19-2008, 03:44 PM
You can use one to tone out CATV outlets in the home. If for some reason you needed to identify which wire was which at the splitter.

Bronco Rob
01-20-2008, 04:33 PM
No Sheeetttt.:beer

Rob, I truly can say that for those of us "electrically challenged", I salute you. :beer

I'm not a moron with electrics, but use of my multimeter, which I think is the exact one you are showing (mine is from HF as I recall)....I really needed some help understanding how to use the thing. I want to start with measuring my battery, ign. off, and then motor on, so I can see what the batt and alt look like (not worried, since everything seems normal). but I also want to be able to check house voltage and what not,, and frankly just don't understand how to use the damn thing and am scared to get shocked.:doh0715:

feel free to continue to show how to use this instrument properly and safely.:chili:

once i find my software disk for my camera, i will grab some pictures of how i do things around the house. It's not necessarily the way everybody does it, but i will get visuals for you guys.

SigEpBlue
01-20-2008, 04:50 PM
You might want to include a part about being doubly sure that if you probe voltage around the house, i.e. single-phase 120VAC, you're not plugged into the high-current ammeter probe sockets OR that your meter is not set to test resistance or current; anything but probing wall sockets with the probes in the VOM sockets and the meter set to measure AC voltage will be potentially dangerous. Not likely to kill you, but better safe than sorry, right?

Bronco Rob
01-20-2008, 05:30 PM
You might want to include a part about being doubly sure that if you probe voltage around the house, i.e. single-phase 120VAC, you're not plugged into the high-current ammeter probe sockets OR that your meter is not set to test resistance or current; anything but probing wall sockets with the probes in the VOM sockets and the meter set to measure AC voltage will be potentially dangerous. Not likely to kill you, but better safe than sorry, right?

yea i did kind of touch on that, i am installing my camera softare right now gonna take some pictures.

any requests Sig? i know you want see my boy bits, feel free to admit it.

:toothless

Bronco Rob
01-20-2008, 07:11 PM
Added information:

My Multimeter:

http://www.supermotors.net/getfile/602016/fullsize/s7300370.jpg

i bought an accessory kit for it that came with a bunch of add on leads:

http://www.supermotors.net/getfile/602022/fullsize/s7300379.jpg

I made "jumpers" with gator clips, these things help out a ton when troubleshooting a circuit:

http://www.supermotors.net/vehicles/registry/media/602023

How to test a simple 120 VAC House outlet:

Step one:

Make sure you're leads are plugged into the right holes.

http://www.supermotors.net/getfile/602025/fullsize/s7300383.jpg

Red Lead to the (V) (Ω) hole

and black to the (COM) hole.

Step 2:

Find 120 VAC outlet:

(ignore the walls, we stripped 1960's wallpaper about a year ago and Mom is still trying to decide what she wants to do with the walls)

http://www.supermotors.net/vehicles/registry/media/602018

Normal household plugs should be three-pronged, polarized (one prong bigger than the other) grounded (single hole) outlet.

Step 3:

Insert Leads:

http://www.supermotors.net/getfile/602019/fullsize/s7300377.jpg

There is some argument about the theory of this, some say that the red lead needs to go the bigger slot and the black lead is supposed to be in the smaller hole.

AC is Alternating Current, the current from each wire, switches back and forth constantly. What it comes down to is, either way you put the leads in, you're going to get a reading. In my opinion it truly doesn't matter. (That's with AC circuits only, if you switch leads on a DC circuit, you'll get a (-) negative sign before the reading. In most cases, the reading is absolute. If you're reading DC current with an analog meter, don't mess up polarity, you can damage the analog meter)

Step 4:

Take reading:

http://www.supermotors.net/getfile/602020/fullsize/s7300378.jpg

This specific outlet reads 121.3 volts. Electricity is theoretical. 120 Volts doesn't always mean 120 Volts can actually read as low as 115, and i have seen it as high as 125. Most electrical applications are designed with a range in mind. So if you're not getting 120 volts exactly, don't fret, it's when you get below 100 volts or about 130 volts that you have to worry.

Why this isn't considered a short:

A short, in AC power, is considered direct white wire (neutral) to black wire (hot), or white or black to ground.

But isn't this direct white to black you ask? No. If i stuck a piece of wire in the outlet, that is considered a short. The difference is that there is resistance in my meter. The only thing that stops a circuit from being a short is a component, a resistor, a computer, a television, a light actually complete the AC circuit. In this case it's the multimeter completing the circuit for the carrier voltage.

How to test resistance:

Step one:

Set your meter:

http://www.supermotors.net/vehicles/registry/media/602025

to the little sound wave looking icon. This will make your meter squeal when you have very little resistance.

Step Two:

Test your leads by touching them together:

http://www.supermotors.net/getfile/602024/fullsize/s7300381.jpg

Resistance should be little to none, mine is reading 002 because i just pulled it out of my truck and it is -8 degrees outside with the windchill.

Step Three:

We'll use my jumper as an example:

http://www.supermotors.net/getfile/602028/fullsize/s7300386.jpg

one lead at one end, one lead at the other end, polarity has no play in checking resistance, you're simply checking to ensure the path is clear for the voltage and the current.

The resistance here is very, very limited.

Some Notes:

You cannot check the resistance of an outlet by putting the leads into the outlet like you're checking voltage. It will give you a false reading of continuity. You would have to check each wire independently (the black, then the white)

Checking amperage:

Depending on what kind of amps your checking:

Low Amperage like Mu amps or microamps.

Mu is this symbol:

http://www.oasis-open.org/docbook/xmlcharent/glyphs/100dpi/U03BC.png

i don't know how to type it, so we will use this for future reference uA

and the symbol for milliamps is mA

mA and uA are very small form of current, usually found in electronic devices powered by DC current. like Computers and Televisions. I am not sure if it's found in vehicles or not, most everything i have come across is 1 amp, so far, i would imagine the innards of a computer would be low current draw

anyway, i don't have an open circuit to test. So i will just show you how to set the meter leads up:

uA or mA:

http://www.supermotors.net/getfile/602026/fullsize/s7300384.jpg

or anything up to 20A:

once again, don't toy with amperage.

http://www.supermotors.net/getfile/602027/fullsize/s7300385.jpg

Hey Rob, why can't you test the outlet for amp draw?:

Why? cuz there isn't any. My multimeter completes the flow for the carrier which is voltage, but, my meter doesn't draw any current.

In order for current to flow, it has to be used. A meter doesn't use any.

But if i were to test the current draw on a 120 VAC or 12 VDC circuit:

i would break the circuit, imagine cutting the wire, adding my gator jumpers, one to the red lead, through the meter, back out to the black lead, jumped to the other side of the cut.

Current does have polarity. So you have to be careful on what you put where.

Normally when you see a 30 amp fuse in a vehicle:

It usually isn't just one component running off of it. It's usually two or three (two headlights) components.

WHEN TESTING CURRENT FLOW:

Shut the power source off, or disconnect it, prior to breaking into the circuit.

here, i will type it again, and bold it:

Shut the power source off, or disconnect it, prior to breaking into the circuit.

Opening a live circuit is not wise, not safe, and just plain not smart. You definitely need to remove the power source prior to doing it.

Checking Battery voltage and vehicle voltage will come later:

No offense, it's -10 right now with the windchill. i will add some stuff later.

Steve83
01-20-2008, 09:12 PM
Blah-blah Theory (feel free to ignore this if it's confusing or boring) :paper:

* 12V test lights are actually a LOT more useful than most people realize, but since this thread is about meters, I won't confuse the issue. Maybe someone (maybe I) will do another article later about test lights.

* A meter actually does draw a VERY tiny amount of current (it has to in order to measure anything), but with modern digital meters, they draw so little that it doesn't affect most circuits and it's not worth considering. But with the VERY latest logic circuits, even the small amount pulled by a digital meter can affect or even damage the circuit permanently, which is one more reason why new cars (~'05-up) require VERY specialized & expensive test equipment for PCM diagnosis. Older analog meters (needle display) draw a significant amount of current, and are notoriously INaccurate & expensive (compared to digital meters), so there's no reason to ever buy or use an analog meter on an electronically-controlled vehicle. Digital meters' internal resistance is typically above 10KOhm; analog meters are typically below 1KOhm. Inductive meters are an exception, but probably beyond the scope of this thread.

* For the same reason that the meter doesn't constitute a short circuit across the household outlet, a person won't pull enough current across 12VDC (or even 220VAC) to kill himself. Your skin has a LOT of resistance (except when you're sweaty), but your internal organs have even more. To receive a life-threatening shock from a modern car (other than from HID headlights), you'd have to jam probes into your chest to push any current thru your heart.

But 12VDC can still do significant damage to you if you're CLOSE to something that's a better conductor when it shorts. Like if you're holding a wrench on a battery terminal & you accidentally slam it into the opposite terminal. :shocked You can be severly burned by the molten/vaporized metal, or your retinas can be burned by the flash. It's theoretically possible to get a life-threatening ZAP when a high-current short circuit is broken (like from a 12V car battery capable of 1000 cranking amps), but it's not very likely. In any case - it's always wise to AVOID shocking yourself. ;)

*
mA = "milliAmpere", which is 1/1000 Amp (10^-3; reciprocal of Kilo)
uA = "microAmpere", which is 1/1000000 Amp (10^-6; reciprocal of Mega)

IDK if Joe has a font installed that contains the lower-case Mu character, but you can find it in the Windows Character Map program in your Start menu, select, copy, & paste it into your post like this:

μ

If that shows up correctly, it's installed on FSB & on your computer. If it shows as an empty box or nothing, then it's not installed on at least one of them.

* Household voltage will never read exactly 120VAC for several reasons:
1) not all power stations regulate their grids at 120; some aim for 115; some as low as 110.
2) voltage in ANY circuit will fluctuate with the load, and since you're sharing your transformer with not only EVERY device in your house, but possibly as many as 10 other houses, something as minor as switching a light will cause the voltage to change. Power stations are always adjusting their output to balance their load.
3) AC voltage is normally described by its RMS (root-mean-square; a complex formula for deriving a useable value for something whose mathematical average is ZERO), and most meters don't actually calculate RMS. They guess at it, assuming a frequency of 60Hz (the standard for US power grids). So if you're measuring an AC signal that's NOT at exactly 60Hz, your cheapo meter won't display an accurate voltage. And even if it IS at exactly 60, your cheapo meter might not be built QUITE precisely enough to display the true RMS. That's why "true-RMS" meters are so much more expensive (above $50), and they're always labelled boldy as "true-RMS". They also typically include a function for displaying frequency, which is another indicator that you're using a true-RMS meter. That said; an auto mechanic has VERY little need for a true-RMS meter, and $20 is enough for the average home-mechanic to spend on a digital multimeter.

Bronco Rob
01-20-2008, 09:54 PM
jesus steve, don't get that precise.

i am trying to stay basic. At least get people to start with the basics. i don't feel like explaining what Hertz means, grids, power stations, substations and other such wonderful things.

To clear it up since some people seem to have issue with it.

Are you going to get zapped to death working on your car? I personally highly doubt it. But stranger things have happened.

Are you going to get zapped to death working on your house circuits? The possibility and potential is much greater than in an automotive application. Be Careful!

Like Steve said, something as simple as sweating can complete a circuit, and you can get burnt by 12 volt electricity. The whole key to working with electricity is to show it respect. That's the point i was trying to make, if you're always careful, you'll be fine. The instant you get relaxed with it, and start being careless, that's when you'll have trouble.

I am not educated on every single component in a vehicle, especially the newer ones, to safely say that there isn't a component in it that could potentially do damage to you. I don't own anything new. It will probably be 2010 before i own something from 2000. So for me to say "you can't get hurt by anything in a vehicle" would be irresponsible on my part, Steve on the other hand deals with them everyday, so he's going to know them better than me.

I was trying to get you guys to be careful, simply because explaining electricity, current flow and resistance to people who know very little about it can get tricky, there are some people that i deal with that still think the power source in their car is the same as the power source in their house because they plug a battery charger into the wall.

AC power sources and DC power sources do have some of the same theories, but they are definitely two different entities.

Bronco Rob
01-20-2008, 10:09 PM
and just to add note, Steve is absolutely correct. A good portion of automotive electrical issues can be solved with a test light.

I chose a multimeter because i have a few.

78bronco460
01-21-2008, 01:00 AM
Good writeup. I have Fluke 12 and 89 meters and recommend them of you think you need a good one.
Just for the sake of safety I'll add a little suggestion here.
Before you work around ANY power... even 12VDC:
Remove your rings or tape over them or wear some gloves if you can't get em off.
Remove your metal watchband. These are probably the worst.
If you have a Mr.T starter set hanging around your neck take that off too.
If you wear dangly ear rings or other piercings, go on and leave em in, but have a friend running the video camera for us :)

These things can and will contact something grounded and something energized at the same time and make a short circuit, and while 12V won't likely give you much of a shock, the current a battery/alternator produces WILL melt them down while they are attached to your body and it happens very quickly. The points of contact can weld to the object and it becomes impossible to get it free quickly. The burns are horrifying.

Sixlitre
01-21-2008, 02:05 PM
thanks! good to see test equipt. (and tool use) addressed!
btw, here is what Ford says about testing (TPS); Throttle Position Sensor (TPS) Function & Diagnosis TSB 94-26-4 by Ford for 93-95 (http://home.comcast.net/~miesk5/technical_service_bulletins.htm#technical_service_ bulletins.htm)

(one thAng, upper case is by Ford in the SB, not me)
"...CAUTION:
MANY VOLTMETERS WILL AUTOMATICALLY CHANGE RANGES WHEN MEASURING TPS OUTPUT FROM IDLE TO WOT. WHEN A VOLTMETER IS USED TO MEASURE TPS OUTPUT FROM IDLE TO WOT, THE METER SCALES OR CHANGES RANGES AUTOMATICALLY. THERE MAY BE AN ERRONEOUS METER DISPLAY UNTIL THE VOLTMETER HAS LOCKED TO THE APPROPRIATE VOLTAGE READING. THE ERRONEOUS METER DISPLAY DOES NOT REPRESENT A DEFECTIVE TPS.
NOTE: IT IS RECOMMENDED THAT THE "RANGE LOCK" FEATURE ON MANY METERS BE SET FOR CHECKING TPS VOLTAGE.
Use the 0.00 range to measure TPS voltage.
If your voltmeter does not change ranges automatically and the meter is set to millivolt scale when reading full range voltages, the meter display may not indicate a valid value. This can be misinterpreted as an open circuit or suspect TPS. Ensure the meter is set to volts for measuring full range voltage levels..."

Hey Miesk5

you got a line on a cheap digital multimeter with a tach feature on it ? I had one but it just got ripped off along with my charger/booster and code reader (jokes on them, the @$$holes forgot the code book:goodfinge).

Thanks

Sixlitre

Shadofax
01-23-2008, 05:39 PM
jesus steve, don't get that precise.

i am trying to stay basic. At least get people to start with the basics. i don't feel like explaining what Hertz means, grids, power stations, substations and other such wonderful things.

To clear it up since some people seem to have issue with it.

Are you going to get zapped to death working on your car? I personally highly doubt it. But stranger things have happened.

Are you going to get zapped to death working on your house circuits? The possibility and potential is much greater than in an automotive application. Be Careful!

.

:beer

I am following along.

So today I pulled out my HF Multi which looks almost exactly like your yellow one. Keeping it simple is great since I understand basic electrical principal, but this multi came with no real instructions on how to use, and I don't want to get electrocuted.

So today I managed to simply test my 4 yr. old optima red top, engine not started, 12.54V. and check the condition of a couple batteries I have laying around.

I'll probably move on to checking houshold current shortly as well as pulling a few plug wires and checking resistance.

question though Rob just for clarification....on the yellow multi you show, is the lower "COM" plug hole always where you stick the black ground wire in? and then to test either AC or DC voltage the next hole up Vohm mA is to be used for the red lead? It's confusing to me what this hole is for versus the next hole up that reads 10ADC?

Then its just a matter of switching to DCV section for DC stuff and ACV (or V squiggly line on yours) to check for ACV? what happens if forget and attempt to test ACV with multi in the DCV section, you blow multi?:banghead:doh0715:

Steve83
01-24-2008, 12:41 AM
It's confusing to me what this hole is for versus the next hole up...:rolleyes: :histerica You know that's going into the quote thread (http://fullsizebronco.com/forum/showthread.php?t=86532)! :lolup

The 10A DC port goes to a shunt wire via a 15A fuse for high-current measurements. The regular red port goes into the guts of the meter for all other measurements. If you try to check (for instance) 120V AC thru the 10A DC port, the high voltage will (of course) blow the fuse, but the meter won't show anything because it's not looking at that port when you set it to 200V AC. If you try to check a 7A DC draw thru the regular red port, you'll blow the ~.1A fuse that protects the meter.

Bronco Rob
01-24-2008, 04:03 AM
question though Rob just for clarification....on the yellow multi you show, is the lower "COM" plug hole always where you stick the black ground wire in?

Yes. the black lead always stays in the COM plug

and then to test either AC or DC voltage the next hole up Vohm mA is to be used for the red lead?

V= Volts, Ohms = Ω = resistance and mA = milliAmps. That will test for volts AC or DC, resistance and small amperages. Not much if anything in your house measures in milliAmps, that's more for electronics.

It's confusing to me what this hole is for versus the next hole up that reads 10ADC?

10 Amps DC voltage only. Means you have a rather inexpensive meter. Can't test any current flow that is known to be higher than 10 ADC.

Then its just a matter of switching to DCV section for DC stuff and ACV (or V squiggly line on yours) to check for ACV?

Yup!

what happens if forget and attempt to test ACV with multi in the DCV section, you blow multi?:banghead:doh0715:

I don't know your meter. But my meter, if i am testing a DC voltage using the AC voltage setting, i will get real weird readings, sit stumped for a second, realize i am an idiot, then turn the dial to the correct setting.

If i try to test an AC circuit while in a DC setting, my meter beeps at me, it kind of sounds like "yooooooourrrrrrannnnnnnnnnnnnnidddddddddiiiiiioooo t" and shows OL on the digital read out.

All my meters are true RMS meters. I need that for some of the things i get into testing. The "cheap" meter that i used for this is a Craftsman and was around $100, the good meter that gets treated like it's made of gold and rarely comes out of it's case is around $500 with all the accessories i have for it.

I used to work in the plating industry, where i was working with rectifiers that would read things like 8-12 DC volts, and like 50-400 amps depending on which part of the plating process i was in all fed from 3-Phase 480 VAC power.

Chances are Shado, with what you're testing, you'll always leave the red lead in the Ω/v/mA setting. The only time you're going to use the other hole is if you are looking for amperage, and in the backyard automotive application, there really isn't a need for that, resistance and voltage is where it's at. If you have limited knowledge of household electricity, i wouldn't suggest testing amperage in the house either.

bronc_17113
01-24-2008, 06:33 AM
good writeup thanks Rob

Doomsmith
11-22-2009, 08:22 AM
I've recently bought a Digital Multimeter for the purpose of testing the Turn signal lights because I keep blowing fuses for them and my hazards. But I don't know how to do that. I tried reading the above but I don't know where to place the probes to test them. Could you help me out with that?





D2k9!

Northernguy
09-15-2010, 10:39 AM
ADMIN EDIT,
please repost your question in the correct forum.

Thanks.