Headlight Electrical Issue
Thread Starter
Melting Slicks
Joined: May 2006
Posts: 2,590
Likes: 403
From: Nashville TN
St. Jude Donor '09
Headlight Electrical Issue
I have a problem when I turn on my bright lights. The lights will start flashing off and on. I've done some basic troubleshooting, but looking for ideas where to go from here.
- Only occurs when brights are on at the same time
- All 4 headlamps randomly flash off and on
- Only headlights flash, all other interior/exterior lights remain on
- Always occurs when brights are on for 10-20 minutes
- Lights flash regardless if engine is on or off
- Problem is consistently repeatable
I looked at my wiring diagram and it shows the ground for the headlights attaching to the alternator. I looked at my alt and I only have the 12v battery connection plus the 2-wire connector . . . no ground wire from headlight harness. Should I have one there?
Problem seemed to start last year when I finally got all my interior lights working, including the dash lights. At that time I also replaced the tach circuit board and headlight switch. A note on the headlight switch, when the dimmer switch is rotated to the "courtesy lights on" position, they do not come on (courtesy lights do work when door open).
Where should I look next? Do I have a bad ground or bad switch? How can I test/check these?
- Only occurs when brights are on at the same time
- All 4 headlamps randomly flash off and on
- Only headlights flash, all other interior/exterior lights remain on
- Always occurs when brights are on for 10-20 minutes
- Lights flash regardless if engine is on or off
- Problem is consistently repeatable
I looked at my wiring diagram and it shows the ground for the headlights attaching to the alternator. I looked at my alt and I only have the 12v battery connection plus the 2-wire connector . . . no ground wire from headlight harness. Should I have one there?
Problem seemed to start last year when I finally got all my interior lights working, including the dash lights. At that time I also replaced the tach circuit board and headlight switch. A note on the headlight switch, when the dimmer switch is rotated to the "courtesy lights on" position, they do not come on (courtesy lights do work when door open).
Where should I look next? Do I have a bad ground or bad switch? How can I test/check these?
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
Stock headlights?
The headlights are on an automatic resetting circuit breaker, it may be kicking them off, CB may be going bad. Could also be the connections on the CB causing it to get hot.
The headlights are on an automatic resetting circuit breaker, it may be kicking them off, CB may be going bad. Could also be the connections on the CB causing it to get hot.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Thread Starter
Melting Slicks
Joined: May 2006
Posts: 2,590
Likes: 403
From: Nashville TN
St. Jude Donor '09
Thanks Roger. I see it's inside my new headlight switch 
I'll double check the connections and make sure things are snug/clean. The fact that the rheostat isn't working either, maybe a bad switch.
I'll double check the connections and make sure things are snug/clean. The fact that the rheostat isn't working either, maybe a bad switch.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
If you go back in to the switch,try grounding the little brass finger and see if the courtesy lights come on,its possible you have lost the ground to the HL switch housing.
Also I have seen foot operated dimmer switches act like yours,you could try unplugging and jumpering between the blue and the green and see if the HL still flicker.
Also I have seen foot operated dimmer switches act like yours,you could try unplugging and jumpering between the blue and the green and see if the HL still flicker.
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Thread Starter
Melting Slicks
Joined: May 2006
Posts: 2,590
Likes: 403
From: Nashville TN
St. Jude Donor '09
Roger hit the nail on the head. I put a ground on the switch housing and the dome light started working when the dimmer switch is rotated all the way to the "lights on" position. I made a ground strap to the door jamb where the dash ground terminates, but how was it done from the factory? There is a tang on the side of the housing and I just used a large female terminal and plugged it onto the tang. I was hoping this would also fix the issue with the bright lights, but it didn't. I'll try Roger's suggestion for that fix this weekend.
Melting Slicks
Joined: Mar 2008
Posts: 2,023
Likes: 6
From: Austin Tx
A small metal grounding strip is connects the switch to a screw on the speedometer housing. The housing is grounded thru the ground wire in the harness.
It's pretty common with funky headlight issues to have a bad ground connection.
It's pretty common with funky headlight issues to have a bad ground connection.
Thread Starter
Melting Slicks
Joined: May 2006
Posts: 2,590
Likes: 403
From: Nashville TN
St. Jude Donor '09
On a related note, along with troubleshooting the electrical issues, I was also going through the vacuum system and FINALLY, my headlights go up and down like they are supposed to!!!
Here is what I found:
In a nut shell, every part of the system had to be replaced or rebuilt except for the vacuum tank. I'm a Certified Corvette Vacuum Headlight System Professional now!
Here is what I found:
- Bad Vacuum Switch - Headlight switch was new, but would not hold vacuum. Had to play around with the switch housing until I go it to hole vacuum.
- Bad Check Valve - One way valve allowed vacuum to flow in both directions - replaced valve
- Missing Filter - Added new filter
- Bad Relays - Rebuilt both following great advice from forum and one forum member was generous enough to send me another dogbone.
- Bad Accuator Seals - One seal had huge holes in it as well as the dust boot. The other seal looked like it was on its last leg too, but still held vacuum. Replced seals and boots on both.
- Bad Vacuum Lines - A number of the vacuum lines were cracked, so I replaced them.
In a nut shell, every part of the system had to be replaced or rebuilt except for the vacuum tank. I'm a Certified Corvette Vacuum Headlight System Professional now!