I have a 79 F-150 that I had recently posted about having some carb issues, thanks to y'all I was able to narrow it down and solve the issue, now I'm having an issue with my back left brake light. When the truck is in park the brake light works perfectly normal, but when I put it in drive my brake like is ineffective, I think this may be the case for my left blinker as well, but not positive at the moment. Right side works fine, front left works fine, front right works fine, only back left that has issues. I would replace the bulb, but I don't figure that's the problem knowing it works when its in park, so if I can save the few bucks on that I happily will lol. Thanks in advance.

 

Sounds like a bad ground. When I was doing mechanic work I always had a piece of wire with an alligator clip on each end. Clip one end on a good ground like the frame or bumper. And the other end to the socket that the bulb goes into. Insure that the base is grounded. And then test. I found 80% of bad electrical issues was a bad ground. Clean up the socket good.

 

Sweet, I'll try that when I get home after school, thanks man!