My brake light and dome light do not work

[MikeFike]

My brake light and dome light do not work;
I have tested the orange/white leads from the dome, good circuit.
I have tested the brake switch, has a connection.
All lights(head/tail) other than the brake work,,, head, tail, flasher left and right.
It seams to be either in the 'white' wire or a ground problem.
Suggestions, test procedures, etc... would be greatly appreciated. Thanks

[truckeroy]

Check to see if brake switch clears pedal arm when brake applied. Is brake light switch good? Make sure you have good grounds.

[imjeff]

If the tail and signals work it has ground. Sounds like your brake switch.

[ray_mcavoy]

Originally Posted by MikeFike

It seams to be either in the 'white' wire or a ground problem.

The orange wire on the dome light is a constant +12V feed from the fusebox. The white wire on the dome light is a switched ground. Rotating the headlight knob fully counterclockwise should ground the white wire, completing the circuit, and turning on the light.

The orange wire on the brake light switch is also a constant +12V feed that's powered off the same fuse as the dome light. However, the white wire on the brake light switch is not a ground. That white wire is the output from the brake light switch and it should be energized when you push the brake pedal. This white wire feeds into the turn signal switch and from there, power is fed back to the brake lights.

If you're getting power on the white wire from the brake light switch (with the pedal pushed), the brake light switch is okay. But the problem could still be in the turn signal switch even though the turn signals are working okay. The contacts in the turn signal switch are setup so they can override the brake light on one side or the other when the turn signal is in use. So a bad connection in those contacts can keep the brake lights from working.

[MikeFike]

Folks, thanks for all of you help,,, at this point the Dome light is working, the problem was a bad ground some where in my instrument/light switch. I am still working on the back up lights. While working under I noticed a connection on the hump above the gas pedal, can someone tell me this connects to? No missing parts missing from my assembly ).

[ray_mcavoy]

That connector is part of the back up light wiring.

There should be a light green wire running from the back up light switch to that connector. And from there, another light green wire runs down under the truck, along the frame, and plugs into the wiring going to the back up lights.

[MikeFike]

Ok, brake lights are still not working(all lights and signals are working). The orange wire to the brake switch gets 12v, when the pedal is not pressed I have 12 v to the white and into and out of the connector, when I press the brake peddle the circuit brakes,,, I assume that is correct. I suspect the problem is in the signal module in the column / horn unit.
The horn does not work, but I have not to working on that yet.
Questions;
Should I test other area,s before I pull the steering wheel?
How do I switch the switch in the colume once it is pulled?
Is there a picture / instructions of the signal switch/horn assembly in the colume so I can see have it should look,,,, I suspect someone if the switch is not bad it may not be assembled correctly. Thanks for all of the help.

[ray_mcavoy]

Originally Posted by MikeFike

Ok, brake lights are still not working(all lights and signals are working). The orange wire to the brake switch gets 12v, when the pedal is not pressed I have 12 v to the white and into and out of the connector, when I press the brake peddle the circuit brakes,,, I assume that is correct.

Constant 12V on the orange wire is good. However, from your description it sounds like the brake light switch is working opposite of normal. When the brake pedal is back against the switch (plunger pushed in), the contacts should be open ... no power on the white wire (unless it's being backfed by a faulty turn signal switch). Then when you push the pedal, the plunger on the switch moves out and the contacts close, sending power to the white wire.

Originally Posted by MikeFike

I suspect the problem is in the signal module in the column / horn unit.The horn does not work, but I have not to working on that yet.
Questions;
Should I test other area,s before I pull the steering wheel?
How do I switch the switch in the colume once it is pulled?
Is there a picture / instructions of the signal switch/horn assembly in the colume so I can see have it should look,,,, I suspect someone if the switch is not bad it may not be assembled correctly. Thanks for all of the help.

Yes, you could very well have a problem with the turn signal switch. But I considering what I wrote above, I'd recommend doing a bit more testing on the brake light switch first.

The turn signal switch can be operated while it's out of the column by simply moving the piece the lever screws onto. Or you could temporarily screw the lever back onto the switch to make it easier to work.

The factory service manuals have some diagrams in them showing how the turn signal switch (and other parts) fit into the column. Check here for some manuals --> http://67-72chevytrucks.com/vboard/s...d.php?t=558016

I don't think the manuals cover the inner workings of the turn signal switch though since those are typically replaced as an assembly.

[MikeFike]

Ray,
Thanks, the switch is correct as you described( When the brake pedal is back against the switch (plunger pushed in), the contacts should be open ... no power on the white wire (unless it's being backfed by a faulty turn signal switch). Then when you push the pedal, the plunger on the switch moves out and the contacts close, sending power to the white wire.
), I probably did not do a good job describing. So I will pull the steering wheel. I was hoping to see how a correct canceling switch and horn rind, button, etc... looked correctly in the column,,, I suspect it may not be installed correctly,,, before I order a new turn signal unit.

[ray_mcavoy]

Okay, sounds like your brake light switch is okay then.

I don't have any pics handy showing how the parts fit together but here are a few threads with some pics that might be helpful:

http://67-72chevytrucks.com/vboard/s...d.php?t=456674

http://67-72chevytrucks.com/vboard/s...=329597&page=2

http://67-72chevytrucks.com/vboard/s....php?p=6534999

[MikeFike]

ray_mcavoy,
,,, thanks for all of your help. The brake lights are working! I had to disassembled the turn signal unit and give it a good cleaning with contact cleaner, that took care of it.

[ray_mcavoy]

You're welcome! Glad to hear that you got the brake lights fixed!