No turn signals / brake lights
 

1977 C30 Dually, LS swapped. ALL lights are LED. All were working before the swap down time.

UPDATE: Unplugged both the headlight switch and the brake switch. Nothing changed. Front marker lights and taillights are getting a trickle of voltage from somewhere and won't turn off. PULLED Brake/Hazard light fuse and it turned them off. Why would that circuit be getting power with nothing on??

Sometime during its down time the turn signals and parking lights stopped working, brake lights and headlights worked.
After some diagnostics and replacing the headlight switch and it's melted pigtail, I got some of it working.

All of the sockets light up except the backup lamps. They're not getting power from the main harness. If I power their circuit independently at the rear harness plug, they work fine.

Current status:
Key OFF / Lights OFF - Dim taillight and front marker lights still on (even unplugging the headlight switch won't make them turn off)
Brake Lights work

Key ON / Lights OFF - Dim taillight and front marker lights still on (even unplugging the headlight switch won't make them turn off)
Brake Lights work
No turn signals

Key OFF / Parking Lights ON - Parking lights/Cab Lights work (except fron
fenders
Brake Lights ON - even w/o pedal depressed
No turn signals

Key ON / Parking Lights ON - Same as above
Key OFF / Headlights ON - Same as above
Key ON / Headlights ON - Same as above


Any of this indicative of a specific component?
Brake switch is the only part I changed (for TCC lockup)
Original harness isn't hacked up...except...

At the rear harness there are brown wires for the marker lights, license plate lights etc. The harness has one of those that was grounded with a non-factory spade connector and wire plugged into it's factory male connector. (it has 12v on it, I have no idea how it was working before, I've unplugged it now). I see no corresponding factory plug to go to it (it looks exactly like the one for the rear fender marker lights.)

Any guidance is appreciated.

Re: No turn signals / brake lights
 

The wiring diagram is your best friend.

Quote:

At the rear harness there are brown wires for the marker lights, license plate lights etc. The harness has one of those that was grounded with a non-factory spade connector and wire plugged into it's factory male connector. (it has 12v on it, I have no idea how it was working before, I've unplugged it now). I see no corresponding factory plug to go to it (it looks exactly like the one for the rear fender marker lights.)

Here is the rear of the truck wiring per the manual. If it doesn't look just like this it's not going to work.
:chevy:

Re: No turn signals / brake lights
 

Thanks for the reply and the color diagram. It's all working now. I think it was a combination of the all-LED system not having enough resistance in combination with a sketchy turn signal switch.

In your diagram, my rear harness is exactly like that except that it had one more brown pigtail in the marker/license plate lamp section. I couldn't for the life of me imagine what it went to but maybe it went to the lamps on the tailgate (it's a dually) that a previous owner deleted. That's my best guess.