I spent two months diagnosing, fixing, cleaning and replacing to get all the electrical lights and accessories working on my 81. Got everything operating properly. Well after about four months now some of the Gremlins have resurfaced.
My dash lights went out and would occasionaly flicker and come on. I had already replaced the printed circuit, bulbs and cleaned the connectors and all was well. So last Friday night I replaced the light switch with a GM NOS switch. Everything was back to working again until I came home at night from the cruise night Sat night. The dash lights did not come on when I turned on the lights even twisting the dimmer. After about 10 minutes they came on and dimmed just fine. I stopped for fuel turned the lights on and the same thing happened. I am baffled now.
Also replaced both the door lock switches, rewired the grounds and installed new actuators. Everything was working fine then a few weeks ago they would only lock with the switch and not unlock and some time they will unlock and not lock.
I had cleaned the joystick and switch for the mirrors and had them working fine on both sides. Now sometimes they work in one dorection and not another. I just got a new joystick, well see if that solves the problem.
I'm beginning to think GM hired Lucas to design the electrical system for the C3's.
I suspect I'm not the only one having these issues, chime in!

 

there may be a different design than a early c3, but i had a similar problem on my 72. the headlight switch was pushed up too tightly to the dash pad, and was making intermittent contact. make sure the wiring harness is completely seated in the switch.

 

Just had a similar thing with my lights. Finally narrowed it down to a a minuscule cut in a wire that was contacting the metal clip it the wire sits in. Electrical tape around the exposed wire, ( I had to squint to see the exposed wire, that's how small it was) put the wire back in the retainer, resealed the retainer with some elec tape. Checked everything before closing everything up, all is good. Patience was my best friend for this one. Good luck.

 

The next time the dash lights act up touch a test light to the "Inst light" fuse and see if there is power there.
The fuse is in the middle of that circuit,that will give us a direction to go.