Electrical Issues!
 

Ive got a 78 GMC C25 Im working on getting some bugs worked out of. So here are my issues;

The turn signals hyper flash, and the bulbs are standard halogen bulbs. The left side will work, hyper flashing, and when the right side turn signal is put on, sometimes all four flash, sometimes not. The turn signal lever does not seem to effect it, it is a new part.

This is a customer's vehicle, from what he says it seems that this issue was present before rebuild the column.

Additionally, the gauge cluster does not light up when the headlight switch is pulled. He says the circuit board is new, and headlight switch is new too.

Any ideas?

Re: Electrical Issues!
 

Sounds like a grounding issue. That’s usually the first and easiest to check. From there, check for an open/bare wire somewhere within the light harness.

Re: Electrical Issues!
 

Halogen? For turn signal bulbs?

Instrument cluster often shares a fuse with the running lights. But not the turn/brake lights. Since you have issues with the turn lights, possible that is also causing issues with the dash lights.

Re: Electrical Issues!
 

So far I have determined the headlight switch is the culprit for the dash lights (swapped with a good one from my 67), still working on the turn signals. What I mean by halogen is just non-LED. Not sure of the correct term.

Re: Electrical Issues!
 

Usually if your getting the hyper flash with the blinker bulbs, one of the bulbs is bad. If you swap out all the bulbs and your still getting the hyper flash, then on of the connectors for the lights is bad.
I had that on my truck when I first got it. I changed out all the bulbs, but I ended up changing out the connections for the marker lights in the grille, and that fixed it. Someone had poorly spliced them in, plus the connectors themselves just looked bad. Like they had gotten pretty hot at one time or another.

Re: Electrical Issues!
 

I will check and post my results. Thank you!

Re: Electrical Issues!
 

Your welcome, and good luck. Electric issues can be a pain chasing down. I know a little about chasing down issues. I worked in the repair dept at an auto factory for years. Bad grounds, cut or pinched wires were the bulk of the causes.

Re: Electrical Issues!
 

Good find on the headlight switch. I am a big fan of 'known good parts' as a troubleshooting technique.

It was a lot simpler before halogen and LED muddled the terminology waters. As long as you had the proper number bulb, it just worked. I was worried that your customer had tried to fit halogen(normally pre-LED headlight type bulbs) in the turn signal spots as some kind of super bright custom job. That could cause all sorts of issues with standard flasher cans.

Does the emergency flasher switch make all four corners flash? I use that as a quick check for the turn bulb filaments and connections.

Re: Electrical Issues!
 

Yes, the emergency light makes all the proper spots flash, honestly Im curious if I am having an issue with one of the flashers on the fuse block. SOMETIMES when starting a turn signal, or 4-ways, they will blink the appropriate for 1.5 flashes, then go fast.

Re: Electrical Issues!
 

Update - so as far as dash lights go, the headlight switch was the culprit.

But onto the turn signals. I have found numerous poor ground spots and connections, and have since replaced with proper fittings and weather tight shrink wrap and such.

I have found a wiring diagram for the rear harness, and followed. Found that all six bulbs shared one ground and it should be one ground per side, so I did so, and the harness photo indicates the rear harness should have a crossover ground (tying both L & R together, still grounding once on each side) and I have found some solder spots that look OK, not thinking theyre the culprit. Still flashing fast. Attached is a pic of the harness Im following.

Re: Electrical Issues!
 

Success! I swapped the flasher in the fuse block for a known good one from my 84, and they flash as they should. BOTH of the flashers had gone bad, seemingly at the same time. My guess is when this gentleman did his column rebuild, he left everything hooked up and overloaded them or something. Or they both just gave up the ghost together.

Re: Electrical Issues!
 

Happy you fiqured it out, good job!