# Brake light issue ugh..help please



## Frustrated GTO guy (Jul 6, 2020)

My 1966 GTO has an issue with the brake lights all the tail lights work all the turn signals work I replaced the brake light switch underneath the pedal and still having an issue . I know that my fuse is good because my tail lights and signals are working properly.I've also checked the power going to the brake light switch which is good. Anyone else have this issue or can leave me to fix this problem so frustrating


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## PontiacJim (Dec 29, 2012)

Sounds like a ground issue if all of them do not work.

Using a test light, and following your wiring diagram, do you have power going back to the brake lights when the pedal is applied?

Go step by step using a test light, not just replacing parts. Power to the brake light switch going in? Brake light switch adjusted correctly to the pedal? Power back out of the brake light switch when you depress the brake pedal or switch "button?" Dome light working?


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## Frustrated GTO guy (Jul 6, 2020)

PontiacJim said:


> Sounds like a ground issue if all of them do not work.
> 
> Using a test light, and following your wiring diagram, do you have power going back to the brake lights when the pedal is applied?
> 
> Go step by step using a test light, not just replacing parts. Power to the brake light switch going in? Brake light switch adjusted correctly to the pedal? Power back out of the brake light switch when you depress the brake pedal or switch "button?" Dome light working?





PontiacJim said:


> Sounds like a ground issue if all of them do not work.
> 
> Using a test light, and following your wiring diagram, do you have power going back to the brake lights when the pedal is applied?
> 
> ...


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## pontrc (Mar 18, 2020)

X with Jim ,Are you’re hazards working? Usually the brake ,hazard,are on a separate circuit than the tails blinkers.Also the dome light is on the brake circuit


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## Frustrated GTO guy (Jul 6, 2020)

How would I know which one is the ground wire what color would it be there's a lot of wires back there


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## Frustrated GTO guy (Jul 6, 2020)

Doesn't have hazard lights but the blinker on both sides works. The dome light never worked


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## pontrc (Mar 18, 2020)

Forgot 1966 on the hazard sorry about that


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## Frustrated GTO guy (Jul 6, 2020)

pontrc said:


> Forgot 1966 on the hazard sorry about that





pontrc said:


> Forgot 1966 on the hazard sorry about that
> [/QUOTE
> 
> 
> ...


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## GTOJUNIOR (Aug 7, 2011)

A service manual is recommended, for things such as this.
It the meantime here is a color-coded schematic to trace the grounds.
Check all the grounds and bulbs first, If the problem persists it could be the signal switch.
Cheers.


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## pontrc (Mar 18, 2020)

Do not get frustrated Frustrated.These cars are like therapy away from the honey do list.Take a nice cup of coffee look at JRs diagram and take it one step at a time.look at the diagram first with coffee and if that does not work out try it with a beer or 12


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## tDub (May 6, 2018)

I have a 66 conv, but havnt had that problem with it, but with a ford pickup. As we know there are two filaments in the bulb; the tail is separate (usually the smaller one) the blinker and brake share the same (larger brighter one) if the blinker is working then there is no ground problem at the bulb socket as there is usually only one ground wire for each socket. check that to see there is only one ground; as I recall there are three wires to each socket (ground, tail, brake/blinker)
I would check to see that brake switch circuit under the dash is sending a signal thru to the bulbs. The turn signal switch may be the culprit; it allows both l &r rear bulbs to light when in the neutral position and brake is applied; when you put that switch in the left turn position it blocks a blinking signal from going to the right bulb and vice versa. so one side blinks, and the other if you are applying the brake, stays lit with no blinking. if the unblinking side is not lit, then a either a ground or the 12volts side is broken someplace in the brake circuit; Be sure not to overlook the simple stuff; although its a new brake switch I would check continuity of that and the old switch; also be sure if you have voltage to the switch; you should be able to perform tests with a small VOM, to check voltage and using it as a continuity checker; the blinker switch was the problem in my pickup. also you did not mention if this is a recent problem, or something you have been dealing with for a while; small water leaks from the windshield channel can wreak havoc with the under-dash wiring. use the circuit diagram; I would print it out then go to a copy place and enlarge it about 4x so you can trace with a pencil; stop by walmart and buy a colored pencil set, they come in real handy when trying to trace a curcuit.


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## 67 ragtop (Jun 15, 2020)

Frustrated GTO guy said:


> My 1966 GTO has an issue with the brake lights all the tail lights work all the turn signals work I replaced the brake light switch underneath the pedal and still having an issue . I know that my fuse is good because my tail lights and signals are working properly.I've also checked the power going to the brake light switch which is good. Anyone else have this issue or can leave me to fix this problem so frustrating


it may be as simple as adjusting the switch to the pedal. pull the switch, and try it manually with the wires hooked up 
and see if that works good luck


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## 67 ragtop (Jun 15, 2020)

it could as simple as a switch adjustment @ the pedal take the loose while wired up try to
operate it manually the switch may be to close to the pedal good luck


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## Frustrated GTO guy (Jul 6, 2020)

tDub said:


> I have a 66 conv, but havnt had that problem with it, but with a ford pickup. As we know there are two filaments in the bulb; the tail is separate (usually the smaller one) the blinker and brake share the same (larger brighter one) if the blinker is working then there is no ground problem at the bulb socket as there is usually only one ground wire for each socket. check that to see there is only one ground; as I recall there are three wires to each socket (ground, tail, brake/blinker)
> I would check to see that brake switch circuit under the dash is sending a signal thru to the bulbs. The turn signal switch may be the culprit; it allows both l &r rear bulbs to light when in the neutral position and brake is applied; when you put that switch in the left turn position it blocks a blinking signal from going to the right bulb and vice versa. so one side blinks, and the other if you are applying the brake, stays lit with no blinking. if the unblinking side is not lit, then a either a ground or the 12volts side is broken someplace in the brake circuit; Be sure not to overlook the simple stuff; although its a new brake switch I would check continuity of that and the old switch; also be sure if you have voltage to the switch; you should be able to perform tests with a small VOM, to check voltage and using it as a continuity checker; the blinker switch was the problem in my pickup. also you did not mention if this is a recent problem, or something you have been dealing with for a while; small water leaks from the windshield channel can wreak havoc with the under-dash wiring. use the circuit diagram; I would print it out then go to a copy place and enlarge it about 4x so you can trace with a pencil; stop by walmart and buy a colored pencil set, they come in real handy when trying to trace a curcuit.


But the blinkers work fine and the taillights all work. This just happened it was working fine a week ago. I've tested the brake switch. It lights up when I use a test light. I pulled it out and use my finger to push it in and out. 
No brake lights. Would the turn signal switch be a issue if the blinkers all work. ?


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## Frustrated GTO guy (Jul 6, 2020)

Frustrated GTO guy said:


> But the blinkers work fine and the taillights all work. This just happened it was working fine a week ago. I've tested the brake switch. It lights up when I use a test light. I pulled it out and use my finger to push it in and out.
> No brake lights. Would the turn signal switch be a issue if the blinkers all work. ?


 There is no way I'm taking to a shop to get robbed again.


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## Bruce Elias (Mar 7, 2012)

So the guy that mentioned the switch adjustment might be on to something... the directionals and brake lights work independent of each other.. So even tho your directionals work, snd you tested the switch with a meter, if the switch is pushed in too far, when you step on your brake pedal the contacts aren't going to touch.. he suggested to pull the switch all the way out of the adjustment and leave it connected to the plug...your brake lights should work push the switch in with your thumb and see if they go out...if so, just push the switch back into the housing and in just far enough until the lights go out, and when you press the pedal, they go on again.....
if that doesn't work, check the ribbon cable that runs from the fuse box back to the trunk harness... it runs under the rug, but you should be able to see where it plugs into the trunk harness from inside the driver side of the trunk...
good luck


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## Bruce Elias (Mar 7, 2012)

sorry didn't see the rest of your last post about pushing the switch in and out, already try wiggling your ribbon harness connections in the trunk and the bottom of the fuse box


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## GTOJUNIOR (Aug 7, 2011)

FWIW; 
I had a similar issue a few seasons back were my stoplights would stop functioning while every other light functioned as intended.
After a few tests/checks, finding no real issue, it would work for a while and then would act up at random. 
I would be out driving and have someone tell me I have no brake lights, UGH!
During this, I went through several aftermarket switches, replaced the connectors, and so on. 
If I disconnected the switch and hand-tested them, they would work. Re-install and a few days later no good??
Never did pinpoint the exact issue but it took several switches to finally get everything to function. 
I guess just another case of AFTERMARKET JUNK SYNDROME!
Cheers.


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## Montreux (Mar 8, 2009)

The brake light circuit is routed through the turn signal switch. Looking at the circuit diagram, the “cold” side of the brake switch is the white wire to the turn signal switch. The green and yellow wires go from the switch to the brake/turn lights.

With no turn signal, you should have continuity between white, yellow, and green.
In left turn position, yellow wire gets connected to flasher. Green and white wires should show continuity.
In right turn position, green wire gets connected to flasher. Yellow and white should show continuity.


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## 67 ragtop (Jun 15, 2020)

as bruce suggested about the ribbon harness go to the trunk and disconnect the harness and test to see
if you have power and if so continue on down the harness into the trunk until you hopefully find the bad spot. 
if you have power at the ribbon harness you may have to change the harness for the tail light assembly.


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## Paul Schiavon (Apr 22, 2014)

Frustrated GTO guy said:


> My 1966 GTO has an issue with the brake lights all the tail lights work all the turn signals work I replaced the brake light switch underneath the pedal and still having an issue . I know that my fuse is good because my tail lights and signals are working properly.I've also checked the power going to the brake light switch which is good. Anyone else have this issue or can leave me to fix this problem so frustrating


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## Paul Schiavon (Apr 22, 2014)

Hi frustrated, I had the same problem when I bought my 1966 GTO Convertible, On the way home people were almost rear ending me when I was braking. Checked car out Tail and Turn Signals worked fine, same as your car. It turned out that the Turn Signal Switch on the steering column was the problem. You replaced the brake switch and verified +12VBAT on the orange (hot side) feed wire, correct?, if so, check for potential on the white (cold side) wire from the brake switch by depressing the brake pedal. If the brake switch is installed properly, the white wire should have +12VBAT potential present when the brake switch is depressed. If that checks out, it can only be one of two things causing this problem: 
A) Check out the connector from the dash harness to the steering column ("C" shaped connector) to verify that the connector is securely snapped together. If it is secure, then see "B" below.

B) If the aforementioned "C" shaped connector is securely snapped together, the problem is the Turn Signal Switch on the steering column. The reason is: Turn Signal switch when no L or R directional is in use should show continuity from the white wire from the brake switch to the yellow wire (left rear Turn/Brake light) and to the dark green wire (right rear Turn/Brake light). When no turn signal is in use, you hit the brakes and the white wire feeds the yellow wire to (3) LR tail lamps and also feeds the dark green wire to (3) RR tail lamps. When you hit the left directional, the violet wire (cold side of 552 flasher) feeds the yellow wire to LR tail lamps (while the white wire shows continuity to the dark green wire (RR Turn/Brake Light). When you hit the right directional, the violet wire (cold side of 552 flasher) feeds the dark green wire to RR tail lamps (while the white wire shows continuity to the yellow wire (LR Turn/Brake Light).

The failure in the steering column mounted turn signal switch is as follows: the turn signal switch internally is not showing continuity to the white wire from the cold side of the brake switch, thereby failing to feed power to the LR and RR tail lamps when the brakes are applied, (The turn signals work because the violet wire (cold side of 552 flasher) connection to the turn signal switch is good and the turn signal switch (in directional mode) is working.

This is a frustrating problem because you can test the directionals and they work (proving the wiring on the yellow and dark green wires to the rear lights on the car). This normally means the brake lights should work too. In my case and I suspect your case the brake lights are inoperative due to a defective turn signal switch.

Ames Performance Engineering has all variations (Boyne vs Delco) (Tilt/Non Tilt column) on page 168 of the current catalog number G35 of the GTO directional signal switches. Verify your existing switch (Boyne or Delco) before ordering a new switch.


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## Lemans guy (Oct 14, 2014)

Try a new different brake light switch, have had new ones test like they work with a ohmeter, ...push with finger in shows correct off.......let out shows continuity....light should be on...

but switch will not carry the current to the brake light, it will work the meter or test light..

I think they are cheap internally and have too much resistance to carry the load, but enough to run test light....so try another new switch....$7 or $8 bucks


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## tDub (May 6, 2018)

no need to go to the dealer if replacing the turn signal switch; its really not that hard with the right tools; go to oreilly or autozone and rent the steering wheel puller; just proceed slowly and take pix each step for reassembly; (If you own a car like this you should have in your library a copy of the factory repair manual; if not search online; it will have step by step instructions for dealers to use when repairing most everything on the car. Actual factory manuals are usually expensive , but reprints are available.) the turn switch is crammed in there but can be removed, It should be pretty self explanitory; if not sure go to utube for a video most older cars are the same so it could be any gm car; usually by now the self cancelling feature may have broken anyway so a new switch tor that alone would be worth changing the switch; before anything check ALL connectors for corrosion- it builds slowly then one day somthing stops working; clean with a small brass brush and electrical cleaner; DISCONECT BATTERY FIRST!


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