No Brake Lights - FSB Forums
Register Home Forums Active Topics Photo Gallery All Albums Mark Forums Read Auto EscrowInsurance FSB Store
FullsizeBronco.com is the premier Ford Bronco Forum on the internet. Registered Users do not see the above ads.
Reply
 
Thread Tools Display Modes
Old 07-12-2012, 01:14 PM   #1
AbandonedBronco
Big Six
 
AbandonedBronco's Avatar
 
Join Date: Feb 2006
Location: Boise, ID
Posts: 2,239
iTrader: (1)
Bronco Info: 1981 300ci 6cyl w/4bbl conversion. 4spd manual
No Brake Lights

Hi all,
The brake lights in my '81 just went out. I haven't had a chance to check the bulbs yet, but I can't imagine both would burn out at the same time (although, I suppose it's possible). I know they were both working a few weeks ago.

The running/tail lights still work. Just no brake lights when I press on the pedal.

I checked the fuses and they all seem Okay.

This is my daily driver, so I know it's just a matter of time before I get pulled over.

I'm not sure where to start digging into this. Any guidance? Thanks.
__________________

1981 & 1984. Both w/ 300 I6. Holley 600 4bbls. 31x10.5" tires. NP-435 trans. 2.5" Exhaust.
Supermotors Pics
AbandonedBronco is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 07-12-2012, 01:36 PM   #2
87SLbronco
Registered User
 
87SLbronco's Avatar
 
Join Date: Jun 2012
Location: Allegan, MI
Posts: 120
iTrader: (0)
Bronco Info: 87 carb fed 5.0L, NP435, NP205, 3.55 gears Stock everything
Check the brake light switch on the brake pedal? It's possible that it worked it's way out of adjustment. I know on my bko if Im under the dash for whatever reason and am not careful I can screw with mine just enough so the switch doesn't make contact when you hit the brakes.
87SLbronco is offline   Reply With Quote
Old 07-12-2012, 05:46 PM   #3
87Roughneck
Registered User
 
87Roughneck's Avatar
 
Join Date: Feb 2012
Location: Gloucester, VA
Posts: 648
iTrader: (0)
Bronco Info: '87 Bronco Custom; 300cid EFI w/ 3" exhaust; 35" Goodyear Wrangler Kevlar MTRs on 15x8; 2.5" lift
Quote:
Originally Posted by AbandonedBronco View Post
The brake lights in my '81 just went out...
I'm not sure where to start digging into this.
Really?

Quote:
Originally Posted by 87SLbronco View Post
Check the brake light switch on the brake pedal?
Yeah, try that.
__________________
"I'll try to be nicer if you'll stop being an idiot."

Quote:
Originally Posted by Steve83 View Post
Is he STILL arguing this? I put him on my ignore list years ago, so I don't have to read his ranting.
Quote:
Originally Posted by TheUnforgiven View Post
Years? He's only been here since February of this year.
Quote:
Originally Posted by TheUnforgiven View Post
87Rougneck knows his shit, even though he can be a dick. I'd listen to him.
87Roughneck is offline   Reply With Quote
Old 07-12-2012, 07:29 PM   #4
AbandonedBronco
Big Six
 
AbandonedBronco's Avatar
 
Join Date: Feb 2006
Location: Boise, ID
Posts: 2,239
iTrader: (1)
Bronco Info: 1981 300ci 6cyl w/4bbl conversion. 4spd manual
Really what?



Either way, the switch is working. However, I ran a voltmeter across it and I'm only getting 2.5v instead of the 12.5v my '84 Bronco is getting.

I'll start tracing it down, but if anyone has any ideas that could speed the process along, I'd really appreciate it.
__________________

1981 & 1984. Both w/ 300 I6. Holley 600 4bbls. 31x10.5" tires. NP-435 trans. 2.5" Exhaust.
Supermotors Pics
AbandonedBronco is offline   Reply With Quote
Old 07-12-2012, 08:27 PM   #5
AbandonedBronco
Big Six
 
AbandonedBronco's Avatar
 
Join Date: Feb 2006
Location: Boise, ID
Posts: 2,239
iTrader: (1)
Bronco Info: 1981 300ci 6cyl w/4bbl conversion. 4spd manual
I'm having difficulty finding it in my Chiltons, can someone tell me where the ground is for the brake lights?
__________________

1981 & 1984. Both w/ 300 I6. Holley 600 4bbls. 31x10.5" tires. NP-435 trans. 2.5" Exhaust.
Supermotors Pics
AbandonedBronco is offline   Reply With Quote
Old 07-12-2012, 10:09 PM   #6
BroncoJoe19
Registered User
 
BroncoJoe19's Avatar
 
Join Date: Jan 2008
Location: North Jersey
Posts: 1,892
iTrader: (0)
Bronco Info: '90 Eddie Bauer 33x12.5 r15 302
Really?

First thing to check, is your bulbs.

I think that they are grounded behind the left tail light assembly.
BroncoJoe19 is offline   Reply With Quote
Old 07-12-2012, 11:19 PM   #7
bronco6696
Registered User
 
Join Date: Jan 2012
Location: edgewater, nj
Posts: 298
iTrader: (2)
Bronco Info: 93 bronco 5.8 cherry bomb glasspacks
Bulbs.. Its behind the drivers tail light.. Another thing to check is where there is a brake light harness screwed into the t fitting on your brake line below the master cylinder on the frame..
__________________
Quote:
Originally Posted by cajunrebel View Post
They are physically larger
bronco6696 is offline   Reply With Quote
Old 07-13-2012, 02:44 AM   #8
Steve83
Registered User
 
Steve83's Avatar
 
Join Date: Jul 2003
Location: Memphis, TN
Posts: 36,274
iTrader: (101)
Bronco Info: '83 VIN & title on '93 frame/body w/'95 4.9L & EB paint
Before anything else, try working the hazard switch a few times.

Joe
Only the defrost grid is grounded at the L taillight; all the taillights are grounded in the engine bay.

6696
The brake light circuit doesn't pass through anything on the frame; what you're seeing is the '93-only SCCDS.
__________________
Walk softly & carry a BIG SIX ! ! !

. .
Steve83 is offline   Reply With Quote
Old 07-13-2012, 09:02 AM   #9
87Roughneck
Registered User
 
87Roughneck's Avatar
 
Join Date: Feb 2012
Location: Gloucester, VA
Posts: 648
iTrader: (0)
Bronco Info: '87 Bronco Custom; 300cid EFI w/ 3" exhaust; 35" Goodyear Wrangler Kevlar MTRs on 15x8; 2.5" lift
Quote:
Originally Posted by AbandonedBronco View Post
Really what?



Either way, the switch is working. However, I ran a voltmeter across it and I'm only getting 2.5v instead of the 12.5v my '84 Bronco is getting.

I'll start tracing it down, but if anyone has any ideas that could speed the process along, I'd really appreciate it.
So, how do you know that the switch is working?

You got 2.5 volts when you went across the 2 terminals of the switch? Is that correct? All that tells you is that you don't have a good voltage source to the switch or that you don't have a ground on the other side of the switch, which is through the turn signal switch, brake light bulbs, etc. You still need to find out which is the problem.

Attach one lead of your meter to a good chasis ground and check for voltage at the brake light switch. If you don't have battery voltage at one terminal, go find out why not. If you do have battery voltage at one terminal, then check to see if there's a good ground on the other, and if not, then chase that problem down.
__________________
"I'll try to be nicer if you'll stop being an idiot."

Quote:
Originally Posted by Steve83 View Post
Is he STILL arguing this? I put him on my ignore list years ago, so I don't have to read his ranting.
Quote:
Originally Posted by TheUnforgiven View Post
Years? He's only been here since February of this year.
Quote:
Originally Posted by TheUnforgiven View Post
87Rougneck knows his shit, even though he can be a dick. I'd listen to him.
87Roughneck is offline   Reply With Quote
Old 07-13-2012, 04:45 PM   #10
BroncoJoe19
Registered User
 
BroncoJoe19's Avatar
 
Join Date: Jan 2008
Location: North Jersey
Posts: 1,892
iTrader: (0)
Bronco Info: '90 Eddie Bauer 33x12.5 r15 302
Quote:
Originally Posted by 87Roughneck View Post
So, how do you know that the switch is working?

You got 2.5 volts when you went across the 2 terminals of the switch? Is that correct?
Yeah, that's how I interpreted that statement too.
I'm thinking that he should have zero volts across the two terminals. If he is getting anything at all, that means that he has a short to ground, (and as you point out, not a good one).
[edit] my thinking was convoluted and wrong... he should have 12 volts across those two [end edit]
BroncoJoe19 is offline   Reply With Quote
Old 07-13-2012, 08:01 PM   #11
Steve83
Registered User
 
Steve83's Avatar
 
Join Date: Jul 2003
Location: Memphis, TN
Posts: 36,274
iTrader: (101)
Bronco Info: '83 VIN & title on '93 frame/body w/'95 4.9L & EB paint
Quote:
Originally Posted by BroncoJoe19 View Post
...he should have zero volts across the two terminals. If he is getting anything at all, that means that he has a short to ground...
No, that would mean he has high resistance in the switch; enough to create a 2.5V drop where it should be 0.

A short to ground would blow a fuse; a poor short (high resistance) to ground creates a hot spot, and may also blow a fuse.
__________________
Walk softly & carry a BIG SIX ! ! !

. .
Steve83 is offline   Reply With Quote
Old 07-13-2012, 11:37 PM   #12
BroncoJoe19
Registered User
 
BroncoJoe19's Avatar
 
Join Date: Jan 2008
Location: North Jersey
Posts: 1,892
iTrader: (0)
Bronco Info: '90 Eddie Bauer 33x12.5 r15 302
lol... this is one of those things that would take minutes to test, and hours to describe how to do it with all the possibilities.

Regarding the ground. Steve says that it is not behind the left tail light. The only location listed in haynes is for a 1992 and newer and that is at the driver's side upper radiator support. The older trucks it doesn't give the location of the grounds.

For a 1981 the black wire to the bulb is the ground. You might try running a separate ground to it to see if that makes a difference.

Again... test your bulbs. If one goes out, the other one has just as many hours on it and is likely to fail soon after the first.

My mind gets fuzzy when I try to wrap it around voltage drop off, but one thing for sure... Steve was right when he said that I was wrong. I was thinking that the brake pedal switch supplied the ground. Nope!

To the suggestions that 87Roughneck offered, I would like to add. Check the brake switch pins for voltage. One should have battery voltage. Then check the other with the pedal depressed. It should also have battery voltage, or just a little less. This is to test the switch, if you do not have the same voltage going through the switch, it is bad.
BroncoJoe19 is offline   Reply With Quote
Old 07-14-2012, 12:10 AM   #13
Steve83
Registered User
 
Steve83's Avatar
 
Join Date: Jul 2003
Location: Memphis, TN
Posts: 36,274
iTrader: (101)
Bronco Info: '83 VIN & title on '93 frame/body w/'95 4.9L & EB paint
Quote:
Originally Posted by BroncoJoe19 View Post
Steve says that it is not behind the left tail light.

Yep - not there.
__________________
Walk softly & carry a BIG SIX ! ! !

. .
Steve83 is offline   Reply With Quote
Old 07-14-2012, 12:26 AM   #14
BroncoJoe19
Registered User
 
BroncoJoe19's Avatar
 
Join Date: Jan 2008
Location: North Jersey
Posts: 1,892
iTrader: (0)
Bronco Info: '90 Eddie Bauer 33x12.5 r15 302
Quote:
Originally Posted by Steve83 View Post

Yep - not there.
LOL... what are you friggin nuts!?
I laughed so hard it brought tears to my eyes :)
BroncoJoe19 is offline   Reply With Quote
Old 07-14-2012, 11:00 AM   #15
AbandonedBronco
Big Six
 
AbandonedBronco's Avatar
 
Join Date: Feb 2006
Location: Boise, ID
Posts: 2,239
iTrader: (1)
Bronco Info: 1981 300ci 6cyl w/4bbl conversion. 4spd manual
Thanks for all the guidance everyone. The less hunting and pecking I have to do is very much appreciated. It's 100 - 110 out, so crawling around inside my Bronco is like working in a sweatbox and the less time out there, the better.

I have two Broncos side-by-side, the other is an '84, so it's nice to compare since its brakes work just fine.

On the '84, if I remove the plug to the switch and check the voltage across the plug, I get 12.5v. If I repeat that on the '81, I get 2.5v.

If I check the plug on the '84 with the negative terminal for the voltmeter on a good frame ground, and the positive to the plug, one wire gets 12.5v and the other gets 0v. (Remember, this is with the plug unplugged from the switch.)

If I repeat this on the '81, one wire gets 12.5v, but the other (which was 0 on the '84) gets 9.5v. Both sides had voltage when it wasn't even connected to the switch.


Would bad bulbs cause voltage problems?

I understand the basics of electronics, but I'm not the best at diagnosing what things mean, so thanks for any help.


Heh, and no, Steve, I'm not seeing any ground there.
__________________

1981 & 1984. Both w/ 300 I6. Holley 600 4bbls. 31x10.5" tires. NP-435 trans. 2.5" Exhaust.
Supermotors Pics
AbandonedBronco is offline   Reply With Quote
Old 07-14-2012, 12:32 PM   #16
Steve83
Registered User
 
Steve83's Avatar
 
Join Date: Jul 2003
Location: Memphis, TN
Posts: 36,274
iTrader: (101)
Bronco Info: '83 VIN & title on '93 frame/body w/'95 4.9L & EB paint
9.5V on the bulb side says the switch isn't connected to the bulbs; it's weakly connected to power. This is for a later truck, but the brake/turn/hazard circuits are basically the same as both of yours:



Did you try working the hazard switch yet?
__________________
Walk softly & carry a BIG SIX ! ! !

. .
Steve83 is offline   Reply With Quote
Old 07-14-2012, 03:22 PM   #17
AbandonedBronco
Big Six
 
AbandonedBronco's Avatar
 
Join Date: Feb 2006
Location: Boise, ID
Posts: 2,239
iTrader: (1)
Bronco Info: 1981 300ci 6cyl w/4bbl conversion. 4spd manual
I did, the hazards work fine.

Thanks for the wiring diagram. That's a little easier to follow than the Haynes manual one.

Are you saying that the connection to the bulbs might have come apart/loose? Would this be behind the taillights?

I'll try tracing the wires by color and see what I can find.
__________________

1981 & 1984. Both w/ 300 I6. Holley 600 4bbls. 31x10.5" tires. NP-435 trans. 2.5" Exhaust.
Supermotors Pics
AbandonedBronco is offline   Reply With Quote
Old 07-14-2012, 03:25 PM   #18
Steve83
Registered User
 
Steve83's Avatar
 
Join Date: Jul 2003
Location: Memphis, TN
Posts: 36,274
iTrader: (101)
Bronco Info: '83 VIN & title on '93 frame/body w/'95 4.9L & EB paint
Quote:
Originally Posted by AbandonedBronco View Post
...the hazards work fine.
That's not the purpose - working the switch several times may clean the contacts, allowing the turn/brake lights to perform normally. If so, buy a turn/hazard switch.

Quote:
Originally Posted by AbandonedBronco View Post
Are you saying that the connection to the bulbs might have come apart/loose?
No, the fault is most likely in the turn switch contacts, or the hazard switch contacts.
__________________
Walk softly & carry a BIG SIX ! ! !

. .
Steve83 is offline   Reply With Quote
Old 07-14-2012, 03:31 PM   #19
AbandonedBronco
Big Six
 
AbandonedBronco's Avatar
 
Join Date: Feb 2006
Location: Boise, ID
Posts: 2,239
iTrader: (1)
Bronco Info: 1981 300ci 6cyl w/4bbl conversion. 4spd manual
Okay, thanks. I'll give that a try. May just pull the steering wheel and clean them. I've had that apart several times (although probably not for a year or more), so I know my way around it a bit. Hopefully that's all it takes.

Thanks for the guidance.
__________________

1981 & 1984. Both w/ 300 I6. Holley 600 4bbls. 31x10.5" tires. NP-435 trans. 2.5" Exhaust.
Supermotors Pics
AbandonedBronco is offline   Reply With Quote
Old 07-14-2012, 03:49 PM   #20
AbandonedBronco
Big Six
 
AbandonedBronco's Avatar
 
Join Date: Feb 2006
Location: Boise, ID
Posts: 2,239
iTrader: (1)
Bronco Info: 1981 300ci 6cyl w/4bbl conversion. 4spd manual
Well, I turned the hazard lights on and then checked the voltage to the brake switch. Every time the hazards "click", the voltage spikes up to 12v and then drops back down to 2v. I'm guessing that's not normal...

Also, when the hazards are on, the front lights blink, but the rears don't. Out to do more digging.



EDIT: Nevermind, that makes sense that the brake voltage would spike with the hazards. It's flickering them off and on.
__________________

1981 & 1984. Both w/ 300 I6. Holley 600 4bbls. 31x10.5" tires. NP-435 trans. 2.5" Exhaust.
Supermotors Pics
AbandonedBronco is offline   Reply With Quote
Sponsored Links
Advertisement
 
Reply

  FSB Forums > Bronco Discussions > Noobie Bronco Tech Questions. Flame free zone!


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -4. The time now is 09:42 AM.


2003-2009 FullSizeBronco.com. All rights reserved