Left Turn signal . doesn't work

Help need advisement! HELP. 1978 GMC K15. Left turn signal when turned on only lights up on dash as a solid light, no blink. Both left side turn signals front and back do not work, Right side turn signal is good. No running lights either side left or right???? in the back of the truck. Brake lights work, Hazzard lights ( 4way flashers) work good. I'm a novice at electrical issue at best. Hoping for some info, so if I have to take it to a shop, I'll at least have an idea. appreciate y'all.

They were working or havent been since you got the truck?

Yes, I also would like to know if they worked previously, if so, when and was anything done right before they stopped working?
Have you checked the fuses below the dash, by the parking brake yet?
We can help, but need to start there first to know more about the situation.

Agreed, need more background. If they were working before and just quit, what were you doing when they quit?

I'd start by checking fuses and grounds first. Bad/dirty/loose grounds can cause all kinds of weird headaches. If all that checks out, I'd replace bulbs. Do the simple things first.

Burned out bulb on the front side marker would be my first check. Then check the grounds. Lights work, fuse is good. Stop/Tail/Turn is one fuse. Have you installed any new lights? or something that needs power?

You can download the 1978 wiring diagram here... https://www.gmsquarebody.com/threads/1973-1991-wiring-manuals.14498/

When checking grounds... they need to be clean (no rust/corrosion) and tight.



Looks like a good connection. wrong. connectors have corrosion inside of them. This restricts the flow of voltage. The flow of electricity is like a garden hose. With all grounds in good condition water flows, if you step on the hose the volume of water goes down. Corrosion is just like that. You then don't get your 12v needed to operate something.

Don't check just the light grounds check body and engine grounds as well.





I would also check the grounds on the taillamps and if you have a trailer harness that too. As a matter of fact, if you have a trailer harness that is aftermarket or PO install. Check that first.

Wrong or bad bulb, bad ground, & sometimes bad socket are usually the cause. So start by checking those first.

I know that sounds strange, but a wrong or bad bulb can cause a lot of weird issues.
-Start by looking at your front left turn signal (under headlight) & the left tail light (especially the dual filament bulb)- both of those are dual filament bulbs & are very important. They also play a role with the running lights.

Other important info to share for help. are you using LEDs? also What happens with turns signal with lights on vs light off.

Sorry for the late response. Purchased truck last July. Everything was working just fine.

Fuses are good and replaced the turn signal relay. Still won't work. I ordered a new steering column switch. Watched some videos.... . Looks like a B***** to replace. Will start looking at the grounds as soon as the weather breaks.

Most likely to be either a bad bulb, or the ground at the turn signal housing. Also check the bulbs to make sure they are oriented correctly (one has two contacts), and are not corroded in the socket.

Got the truck fixed YEAHHHH. had 2 broken ground wires in the left rear side bumper. Pervious owner hacked job a trailer harness. Saving money to replace the whole thing. Thanks again to everyone for the help. Appreciate ya'll