Turn Signal Gremlins

[vanderbilt]

I've got a 1970 C10 with some electrical gremlins in the turn signal/brake light area. Both the front and rear LEFT turn signals work fine when the brake pedal is NOT depressed, but stop flashing as soon as I hit the brake pedal.

In addition, the rear RIGHT light flashes when the LEFT turn signal is on. However, the opposite is not true - only the RIGHT rear light flashes when the RIGHT turn signal is on. A prior owner spliced in a trailer pigtail which might explain some of the issues, but I can't wrap my head around why both rears flash only when the LEFT signal is selected.

Perhaps a related issue is that the hazards work only when the turn signal is on (either side). If you depress the hazards button, nothing works until you put on the turn signal. Is this normal?

I apologize if the issue is fairly obvious - I'm new to troubleshooting electrical issues and my site searches didn't come up with any shenanigans too similar to mine. I have the wiring diagram for the truck, but am so new to electrical issues that I'm not sure where to start. Any advice is appreciated!

[EARNHARDT#3]

Start by replacing the turn signal switch. EVERYTHING runs through it and they do fail fairly often.

[vanderbilt]

Sorry - forgot to mention that I just replaced the turn signal switch. The last one would blow the horn when I depressed the hazard switch...that was sort of an embarrassing discovery. I got the current one from GMC Pauls, so you KNOW it's good!

[cdowns]

check grounds

[LockDoc]

-
.. with Cliff. Read through this thread.....

http://67-72chevytrucks.com/vboard/s...d.php?t=422234

LockDoc

[CastIron]

If somebody has a schematic for the lights this shouldn't be too hard to solve.

[LockDoc]

Originally Posted by CastIron

If somebody has a schematic for the lights this shouldn't be too hard to solve.

All of the wiring diagrams are on here (at the top of the "Electrical" forum)

http://67-72chevytrucks.com/vboard/s...d.php?t=185856

LockDoc

[vanderbilt]

Thanks lockdoc, you beat me to it. The rear right signal is the dark green wire, while the left signal is the yellow wire. It can't be as simple as these two wires crossed or touching, since the right signals work fine.

[LockDoc]

Originally Posted by vanderbilt

Thanks lockdoc, you beat me to it. The rear right signal is the dark green wire, while the left signal is the yellow wire. It can't be as simple as these two wires crossed or touching, since the right signals work fine.

Nope. I'm still betting on bad grounds. Read the entire thread I referenced and install all of the grounds shown..... In your case the engine block to frame and frame to bed would probably be the most important. Then the two bed to tail light housing grounds.

LockDoc

[vanderbilt]

Originally Posted by LockDoc

Nope. I'm still betting on bad grounds. Read the entire thread I referenced and install all of the grounds shown..... In your case the engine block to frame and frame to bed would probably be the most important. Then the two bed to tail light housing grounds.

LockDoc

Thanks - I'll do this first. I know I'm missing both of the grounding straps you mentioned. When checking the grounding on the tail light assemblies, do you simply tape a wire to the negative battery terminal as a test lead and use the ohm setting on the multimeter to determine ground? Any recommendations on the size wire to use for the test lead, or will any gauge do that approximates the gauge of the feed wire?
Posted via Mobile Device

[LockDoc]

Originally Posted by vanderbilt

Thanks - I'll do this first. I know I'm missing both of the grounding straps you mentioned. When checking the grounding on the tail light assemblies, do you simply tape a wire to the negative battery terminal as a test lead and use the ohm setting on the multimeter to determine ground? Any recommendations on the size wire to use for the test lead, or will any gauge do that approximates the gauge of the feed wire?
Posted via Mobile Device

I really can't tell you. I don't use an OHM meter. I just install the grounds and the lights usually work.... Maybe someone with knowledge of that stuff will chime in.

LockDoc