Hey everyone! New to the forum so please let me know if there’s a better thread to post this in.
Anyway getting into my issue…
A few months ago we acquired a 1977 corvette with a bunch of weird electrical “repairs” as well as the typical aging car electrical issues. I’ve started going through a lot of it to sort some things out but I just can’t seem the get the dash lights to work (I’m referring to the bulbs behind the Speedo and tach). One of the lights does come on when I turn the key, I believe it’s the BRAKE light… but beyond that no bright indicator, turn signal indicator or gauge lighting.
I’ve traced it as far back as the fuse box. No power on EITHER side of the fuse, even with the key and light switch in the on position. I’ve seen the switch could be weird so I completely took it apart and cleaned every contact and still nothing.
Ive seen a thread from a forum from years ago with similar issues, but one day it just cut off without resolution so it wasn’t very helpful.
At this point I’m kind of lost and don’t really know where to go now.
Also as I mentioned this is a project and I will definitely be back here time and time again looking for advice. Any help will be greatly appreciated! Thanks in advance.

 

I have a 77 as well. Except I've had mine since Christ was a Corporal.
Step 1. Find and purchase a copy of the Genuine GM Electrical Trouble Shooting Manual for the 77 Corvette.
I'll get mine out and have a look.
OK, got it in front of me, let's have a look.

OK, as you can see. The inst. fuse gets it's power from the headlight switch. So when checking power to that fuse. You need to pull out the switch first.
Now, second, the turn ind. Brake light warning, etc. Lights are on a different circuit. But they also don't work.
Third. What do they have in common?
Answer, they share a common ground.
Check the ground connection at the A piller behind the dash near where the headlight switch is mounted.

 

A little more information for you.


This book
Find one. You'll thank me. Breaks down every circuit and explains how it should work. Individual diagrams. It's like Corvette wiring for Dummies!
and another shot from said manual.

See G901, that's the ground connection your looking for.
hopefully this will get you started in the right direction.

 

You would be wise to buy a Chevrolet Factory Service for a 77 Corvette, they can be found on EBay. Also the AIM (Assembly Manual) is another great resource that shows how the parts were assembled as the car went down the assembly line. Welcome Aboard.

 

Do your tail lights work? those must have power for the instrument lights to work, check the tail light fuse

 

Hey everyone sorry for not responding in a few days. To answer a few questions…
1We do have an assembly manual, has great illustrations of component layout but somewhat lacks in the electrical diagram department.
2. Yes the taillights, brake lights and revers lights work
3. the ground was connected and didn’t seem to have any corrosion and the dash light wiring seemed fairly untouched from the previous owners electrical work.

Looking at the wiring diagram it looks like everything works up to where the switch sends power to the fuse. Which leads me to believe it’s the switch, however as previously mentioned it was dissembled and cleaned. Is there a way I can test that theory before going out and buy a new switch? Possibly putting a jumper wire to bypass the switch? Just don’t want to throw money at something and have the same issues.

 

It's the fact that your indicator lights also don't work that scream poor ground. What about the ground connection at the back of the gauges? As per power out of the switch. Yes I'd certainly try jumping that to get power to the fuse. Then test from there. A bad rheostat in the headlight switch is fairly common. Replacement switches are notoriously poor quality.

 

It’s been a few months but I figured if someone in the future was scanning the internet looking this up, it’d be nice if I could provide an answer.

Threw in a new light switch. Boom. Solved. Rheostat was bad.
I will add however it was touchy at first. One of the fuses (the short one at the very bottom, don’t remember what it is) wasn’t seated very well and would result in the lights not working.

ive also found that the dome light that’s activated by turning the light switch works rather randomly. I believe it’s something to do with a bad cable or connection at the switch end. But for now it works, just something to think about if you have that issue.