Break light problem on my 71 c10

[ole_krusty]

Hey guys I got a problem with my driver side break light it only wants to work when the blinker is on any idea what's wrong??

[Mr Chevorlet]

Most likly a ground issue.

[70LonghornCST]

Did you try replacing the bulb? It may sound silly, but I believe that some bulbs have two filaments and a blinker could work and not the brake light and visa versa depending on what filament is burnt. I moved this thread to the Electrical section where some of our Electrical gurus can say for sure.

[JOHNORO]

had the same issue some time back
I cleaned the contacts and changed the flasher..
it took care of it ... Good luck let us know what happens

[VetteVet]

What you mean to say is that the left brake light only works when the right blinker is on.
The turn signal switch is set up to break the connection to the brake light when that particular side is selected in order for the turn signal to blink. Otherwise it would be a solid light while stopped with the brakes on. The same holds true for the opposite side.

A separate set of points in the TS switch makes the contact for the brake lights when your lever is up or down. It must be that the regular set of contacts for the left brake are bad when the turn signal switch is in the centered position.

To test this, find the steering column connector and locate the white wire in the end of it. With it connected, jump between the white wire and the yellow wire and press the brake pedal. Your drivers brake light should come on.

What you're doing is bypassing the turn signal switch.

[ole_krusty]

Originally Posted by VetteVet

What you mean to say is that the left brake light only works when the right blinker is on.
The turn signal switch is set up to break the connection to the brake light when that particular side is selected in order for the turn signal to blink. Otherwise it would be a solid light while stopped with the brakes on. The same holds true for the opposite side.

A separate set of points in the TS switch makes the contact for the brake lights when your lever is up or down. It must be that the regular set of contacts for the left brake are bad when the turn signal switch is in the centered position.

To test this, find the steering column connector and locate the white wire in the end of it. With it connected, jump between the white wire and the yellow wire and press the brake pedal. Your drivers brake light should come on.

What you're doing is bypassing the turn signal switch.

So your saying its the turn signal switch causing my problem?

[VetteVet]

Well given the details you provided I would say yes.
If the left brake light only works when you turn on the right turn signal.
and the right brake light only works when you turn on the left turn signal then that is normal as long as both brake lights work when the turn signal is off.

I'm assuming that the right brake light works when the signal lever is in the center position (off) and the left turn position, which is normal. Now you are saying that the left brake light does not work with the pedal, if the signal lever is centered, but it will work if you put the signal lever in the right turn position. Is that correct?

The important thing to know is that the brake lights and turn signals share the same wire and bulb filament for each side. The power for the brake lights comes from the brake pedal switch and goes to the turn signal switch via the white wire from the brake light switch.
This is the white wire I indicated in the other post.This wire is connected to both the left and right brake/turn wires(left side is yellow and the right side is dark green). If either one or both of these connections is bad then that side will not work.

When the turn signal lever is placed in left or right turn a separate set of contacts powers
the yellow or dark green wires depending on which turn is selected. The power for the turn signals comes into the TS switch via the purple wire in the steering column connector. At the same time the connection is opened for the respective brake wire on that turn side, and it is closed on the other side for the brake light.
I hope this isn't too confusing.

It's possible that the brake contacts are just dirty on the left side and a good cleaning will solve the problem.

Can you see how jumping the white and yellow wires in the steering column connector would bypass the TS switch and if the brake light works it means the trouble is in the signal switch?

You can also bypass the turn signal switch function by jumping the purple wire to the
yellow or dark green wire and the rear turn light should light. you will have to turn the key on to get power on the purple wire.

If the turn signal works on both sides then the ground is most likely good for the bulbs, especially if the tail lights work ok. I say most likely because I have seen some weird things happen with bad grounds.

[ole_krusty]

Originally Posted by VetteVet

Well given the details you provided I would say yes.
If the left brake light only works when you turn on the right turn signal.
and the right brake light only works when you turn on the left turn signal then that is normal as long as both brake lights work when the turn signal is off.

I'm assuming that the right brake light works when the signal lever is in the center position (off) and the left turn position, which is normal. Now you are saying that the left brake light does not work with the pedal, if the signal lever is centered, but it will work if you put the signal lever in the right turn position. Is that correct?

The important thing to know is that the brake lights and turn signals share the same wire and bulb filament for each side. The power for the brake lights comes from the brake pedal switch and goes to the turn signal switch via the white wire from the brake light switch.
This is the white wire I indicated in the other post.This wire is connected to both the left and right brake/turn wires(left side is yellow and the right side is dark green). If either one or both of these connections is bad then that side will not work.

When the turn signal lever is placed in left or right turn a separate set of contacts powers
the yellow or dark green wires depending on which turn is selected. The power for the turn signals comes into the TS switch via the purple wire in the steering column connector. At the same time the connection is opened for the respective brake wire on that turn side, and it is closed on the other side for the brake light.
I hope this isn't too confusing.

It's possible that the brake contacts are just dirty on the left side and a good cleaning will solve the problem.

Can you see how jumping the white and yellow wires in the steering column connector would bypass the TS switch and if the brake light works it means the trouble is in the signal switch?

You can also bypass the turn signal switch function by jumping the purple wire to the
yellow or dark green wire and the rear turn light should light. you will have to turn the key on to get power on the purple wire.

If the turn signal works on both sides then the ground is most likely good for the bulbs, especially if the tail lights work ok. I say most likely because I have seen some weird things happen with bad grounds.

Thank you for the info and you are correct I'm gonna look into it and hope that is the cause..

Once again thank you.. Zach

[VetteVet]

You're welcome. By the way welcome to the forums.