I installed a new radio in my truck today(78 F150) Did a nice neat install, buttoned everything up. Radio worked!! But now I have no dash lights. I checked the fuse. Tested fine. So I thought headlight switch. Installed new switch. No go. It is only my dash lights out. The high beam light works as does the brake light when you first start the truck. I removed the cluster and unplugged the harness. I am not sure what number is the dash light but there was one wire that showed very faint power when I had my tester on it. I have since unplugged all the wires from my radio install(I used the factory radio harness for my pwr and ground and another green wire that was a constant 12v) Is there a way to jump the headlight switch and dimmer to see if I have power to the dash? I checked a few lights in the cluster and they were fine. Open to suggestions on where to start to fix this!!

 

Looks like we may have found the problem. The original harness is not power and ground. YELLOW with a BLACK stripe is switched 12 volts for power; BLUE with a RED stripe is dash illumination. The latter is often mistaken for ground which is not the case (and is the same circuit you're having problems with). The original radio grounded through its mounting bracket; you'll want to ground your new stereo by tying ground to dash metal.

I assume you did not have issues before the install? How have you verified the dash illumination fuse is good? Turn the parking lights on and turn the headlight **** all the way to the left, and make sure you have 12 volts on both sides of the fuse. Wiring it the way it sounds like you wired it may have also taken out the fuse which would explain why things still didn't work after you undid everything.