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Help please! Single brake light stuck on!

Bronco_007

Jr. Member
Joined
Mar 14, 2022
Messages
132
Loc.
Nature Coast, FL
Howdy, my herd!

My 1974 brake job is complete. I rebuilt the rear drums and converted the front to vacuum booster assisted discs. I tracked down a couple of leaks anfter bleeding the system and remedied them.

I reconnected the battery and immediately noticed one rear brake light was lit. No one was in the Bronco. I hopped in and pressed the brake pedal but the lights did not change. Passenger side brake light is on by itself, driver side is dark. I read a few posts on here and decided to change the brake light switch. Twenty bucks later and I’m still at square one. I used a circuit tester at the driver brake light and got nothing. The battery is new last month. The fuse was replaced last month and still intact. New LED kit from WH about six months ago. LED switches installed under the dash. So I know the battery, fuse, switch, and led light should be good.

Do you think I have a wire issue? Maybe something running from the switch is shorting put between it and the light?

The brake lights were working perfectly before I did the brake job.

As always, toss me a life ring!
 
Last edited:

Tiko433

Contributor
I know just enough to be dangerous
Joined
Jul 9, 2014
Messages
1,787
Loc.
South West Florida
Was it working properly before you did the brake work? The only reason the brake light would be on is the switch is activated. If that’s the case you have two issues. Why is switch stuck on? Why isn’t the other brake light activated?
I brake lights feed through the turn signal switch also. Electrical gremlins suck.
I would check the switch at your brake pedal , make sure it’s installed properly. I would remove the wire connector and see if the light goes off , if it doesn’t some other source is activating it. Then I would look at the turn signal switch.
 
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Bronco_007

Bronco_007

Jr. Member
Joined
Mar 14, 2022
Messages
132
Loc.
Nature Coast, FL
Yes, it worked correctly before. I am concerned I am chasing a short. When my son plugged the battery back in there was a pop under the dash (I was sitting in the truck). I checked and a steel cable (not sure which one) had come loose and was touching the brake switch. I bet that caused my problem.
 

Oldtimer

Contributor
Jr. Member with Sr. moments
Joined
Feb 4, 2005
Messages
824
Loc.
Sunnyvale, CA
May be grounds.
Do both rear running lights work when headlight switch is on?
Do both back-up lights work when trans is in reverse?
Do front & rear turn signals work?
How do brake lights behave when head lights are on?
Do all 4 turn signals work when E-flasher activated?
 
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Bronco_007

Bronco_007

Jr. Member
Joined
Mar 14, 2022
Messages
132
Loc.
Nature Coast, FL
May be grounds.
Do both rear running lights work when headlight switch is on?
Do both back-up lights work when trans is in reverse?
Do front & rear turn signals work?
How do brake lights behave when head lights are on?
Do all 4 turn signals work when E-flasher activated?
Both rear lights work when headlight switch is on.
Back up lights work correctly.
Front and rear turn signals work.
Brake lights do not work when headlights are on.
Flashers work correctly.

Unplugged brake light wires from brake light switch, and they go off. This is the second switch in a week. Same issue with previous switch, which itself worked fine until I plugged the battery back in after completing the new brake kit.
 

Oldtimer

Contributor
Jr. Member with Sr. moments
Joined
Feb 4, 2005
Messages
824
Loc.
Sunnyvale, CA
Yes, it worked correctly before. I am concerned I am chasing a short. When my son plugged the battery back in there was a pop under the dash (I was sitting in the truck). I checked and a steel cable (not sure which one) had come loose and was touching the brake switch. I bet that caused my problem.
LED; with LED relays installed. Worked prior to new break kit without issue.
Have you checked the relays (swap left & right, verify input-output functions, or replaced) since you heard the 'pop'?
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,835
First, cycle the turn signal switch. If it got bumped while climbing in and out during the brakes. The brake light feed goes through the turn signal switch. Next, try cycling the hazard switch. That is the only thing that would have power with the key off that is attached to the brake lights (besides the brake lights, and you already did a switch and being only one side sort of rules that out).

Relays of resistors? Usually it is resistors that are added to make LEDs work with turn signal flashers. You might have relays, but guessing the more normal resistors.
 

rocknhorse76

Contributor
Bronco owner since 1993 💪🏻
Joined
Jun 7, 2014
Messages
342
Loc.
Central WA
First, cycle the turn signal switch. If it got bumped while climbing in and out during the brakes. The brake light feed goes through the turn signal switch. Next, try cycling the hazard switch. That is the only thing that would have power with the key off that is attached to the brake lights (besides the brake lights, and you already did a switch and being only one side sort of rules that out).

Relays of resistors? Usually it is resistors that are added to make LEDs work with turn signal flashers. You might have relays, but guessing the more normal resistors.
^ this ^

I’ve never had much luck with the LED flasher relays. I use the resistors and mount them back behind the taillight buckets.
 
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Bronco_007

Bronco_007

Jr. Member
Joined
Mar 14, 2022
Messages
132
Loc.
Nature Coast, FL
Update:

I have isolated the problem to the position of the new pedal ctonrol rod that goes to the new booster. I removed the switch from the pedal, but left it plugged in; the battery reconnected allowed proper function. I tested the switch and it works correctly, except for when it is attached to the pedal.

So appraently the brake pedal is pressing the switch. Problem is, i measured the distance from the floor to the pedal before i replaced the booster, and the pedal is at the same height now i am done with the install. Yes, the rod going to the new booster is adjustable. But I lifted up on the pedal and that does not remedy it either.

Feeling so dense! Ideas?
 

Oldtimer

Contributor
Jr. Member with Sr. moments
Joined
Feb 4, 2005
Messages
824
Loc.
Sunnyvale, CA
Found one issue: Why one brake light is on all the time, remove brake switch from pedal assembly.
What about other issue: Why only one brake light is on all the time?
And then there is this:
Brake lights do not work when headlights are on.

What vendor did you buy LED bulbs and LED relays from?
Can you post a wiring diagram of how they are connected?
 

m_m70

Contributor
Sr. Member
Joined
Jun 14, 2001
Messages
1,460
Loc.
Pacifica, CA
my brake light switch had the brake lights always on went it went bad. Replaced the switch and all good.

Not sure why you only have one side working.

Are you sure you are installing the switch right??
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,353
As I think was mentioned already, there’s no relationship between a single lamp working and the brake lamp switch.
It’s either all or nothing down at the pedal.

The only things that can make one work, and not the other, begin at the steering column and turn signal switch, and end back at the sockets and bulbs.
It’s strange that it sounds like both lamps work when the pedal is pushed.
That’s very strange indeed.

Hmm, starting to sound like a typical ground problem again!😁
It’s hard to get away from those things sometimes.
 

m_m70

Contributor
Sr. Member
Joined
Jun 14, 2001
Messages
1,460
Loc.
Pacifica, CA
As I think was mentioned already, there’s no relationship between a single lamp working and the brake lamp switch.

Sorry bad wording on my part...Let me try again

I have no idea why you only have one light working. When my switch went bad, my brake lights (both) were on all the time.

My brother in-law installed his switch wrong (placement, not wiring) and his lights were always on.....
 
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Bronco_007

Bronco_007

Jr. Member
Joined
Mar 14, 2022
Messages
132
Loc.
Nature Coast, FL
Replaced turn signal switch.

Now both brake lights stuck on. I removed the switch but left it plugged in and everything works correctly.

So the issue is the switch getting too much pressure when attached to the pedal. Maybe I’ll try removal the poly sleeve inserted in the eye of the push rod going to the booster from the brake pedal. Pedal is same height as before the new brake system went in…

My life!
 
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