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9,130 Posts
Discussion Starter #1
Alright guys, here's my latest issue that I'm having a little trouble with on my own.

My 79 has decided that it wants to have piles of electrical issues lately. First, the starter solenoid went out, then the actual starter hung about a week later (I almost replaced it at the same time I did the solenoid but I cheaped out...). After that I had drained the cheap battery that came on it about three times and it was done (started dumping voltage at start time) so I said the hell with it and put a Yellow Top on it. Here's where our story begins -

I went out to start it the yesterday (after about 1.5 days of sitting) and turning the key got NO reaction. After about five minutes of cussing (I HATE shorts) I boosted it off with the Super Duty and we were on our way.

I started looking at it today and found some interesting stuff.

1) My alternator is overcharging the battery. While running the battery reads 15.x V on my multimeter across the poles. I'm assuming my voltage regulator in the crappy 2G stock alt has bit the dust.

2) When I disconnect one of the cables and test for current, I get about 1 milliamp...Optima says anything under 100 mA is cool. My dome light pulls .9 A and key on is about 12 A... What's up with that, if nothing is measurably pulling my battery down why did it fall on its face? I figured it'd take more than .001 A to completely brick a battery in 1.5 days...


So, questions...

- Is my method of testing for a short effective? This is the first time I've ever tried to hunt for one using a multimeter to check current by disconnecting the hot cable and bridging the two with the multimeter and I'm not entirely sure I'm doing it right since I'm not getting any numbers that suggest a drastic short.

- Could my busted voltage regulator be the source of a possible short? I'm gonna do one of Ryan's 3G swaps on the thing to fix the alt problem and I'm hoping to kill two birds with one stone.

- How much time would it take my 15 V charging system to damage my new Yellow Top? I obviously don't wanna mess that battery up...

Any other advice ya'll? I hate electrical problems :whiteflag
 

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B350 built at THE SHOP
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2,144 Posts
I typically use a test light to verify any significant draws from the battery. A series connection is all that it take. I assume this is what you speak of when you suggest a bridge.
Pull fuses until the light no longer illuminates, or until the meter no longer indicates a voltage small current loads are not easy to detect with the test light.
Often a something as simple as bad diode can cause such a problem while still permitting the alternator to generate voltage. Though the voltage still seems a little on the high side, the battery will drain even if the key is off. Since the alternator cant charge when it does not turn, it means a dead battery when you attempt to start again.

Your current draw or drain seems rather small. have you isolated everything down correctly, and sure that you are not missing some items such as any under dash lights, or the radio memory (if equiped)?

I believe that you are headed in the right direction, and hopefully, the 3G upgrade will solve your troubles.
Regardless, the 3G is probably one of the best upgrades you can make to this era vehicle. Easy as pie to do.
You will also make sure that you wire the keyed portion of this correctly, or you will once again have a battery drain problem:

 

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House of Windsor 4ever!
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10,518 Posts
First, does your instrument cluster have an ammeter? Those can play havoc with the charging system, especially since they're wired in series with the charging wire. Second, the system is overcharging if your charging voltage is above 14.5 V across the battery terminals. Third, if it's that high, you probably have a short in the Field circuit, which would contribute, if not directly cause, the overcharging condition. Fourth, overcharging can boil out a standard battery, but are worse to AGM-type batteries, as there's much less electrolyte in them.
 

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Discussion Starter #4
Thanks ya'll :beer

What kinda irritates me is that this thing has almost no electrical accessories. I killed the dome light, it doesn't have a radio at all, there are no lights anywhere other than the headlights and running lights/blinkers (and they all function properly), the rear window works, etc etc. It did have some ghetto 70s/80s trailer light wiring but when I ripped all of that out today it looked ok...there really isn't much room for it to be having a short.

Well, it quit overcharging. I went on the warpath under the dash and took out some unnecessary fuses like the seatbelt light and if there was a short under there I think I may have gotten it as it sat all day today and maintained a steady 12.55 V from 8:00am to 9:00pm. It was 12.66 V immediately after I killed it the night before, but IIRC it's normal for batteries to drop a little voltage after you just take them off the juice. The only thing that has me a little worried now is that I moved it from the front of the shop to inside the shop (possible rain) and it read 12.42 V when I left it. After about 3 minutes of running with a cold alternator I'd think that it'd have recovered whatever it took to start it (which a simple "bump the key" type of deal, not a long drawn out crank session). I left the hot cable unplugged tonight just in case and I think I'll hook it back up tomorrow morning and check on it at lunch....I really don't wanna screw up this brand new battery.

I'm not sure if the stock gauge is an ammeter or not Andy, it just says "ALT" (really helpful Ford :rolleyes: ) and reads higher than normal when the battery is overcharging. I know the newer ones are ammeters, but IDK about the 78/79 series.

All in all I think I'm gonna order the 3G and try to limit my use of the Bronco until it gets here. I'm not overly happy with the stock alternator anyway, and it's really the last piece of the major electrical systems that I've not replaced.
 
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