Good advice and a freebie diagnostic.
Consistent Headlight Issue
Thread Starter
Instructor
Joined: Feb 2015
Posts: 104
Likes: 0
From: Wichita KS
Consistent Headlight Issue
Early C4 (87) with an annoyingly consistent problem. I've used search and can't find this issue.
When I first turn on lights, both lights always come up fully and headlights work fine. If I stop somewhere for a while and turn the lights off, when I come back, unless it's been a couple of hours, only the driver side light comes up, though both are on. Cycling the lights through an on off process won't help. Only time allows both lights come back up.
Any similar problems or any suggestions to diagnose and fix this?
When I first turn on lights, both lights always come up fully and headlights work fine. If I stop somewhere for a while and turn the lights off, when I come back, unless it's been a couple of hours, only the driver side light comes up, though both are on. Cycling the lights through an on off process won't help. Only time allows both lights come back up.
Any similar problems or any suggestions to diagnose and fix this?
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
You might have a worn gear issue. The only way to find out is to take it apart.
This might be helpful:
https://www.corvetteforum.com/forums...placement.html
This might be helpful:
https://www.corvetteforum.com/forums...placement.html
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
The '84 - '87's have limit switches inside the headlight motors that get dirty. Not a difficult job to clean them. There is lots of information on this procedure on this forum. Use the "search" function at the top of the page. Cliff Harris' write-ups on this problem are excellent.
Thread Starter
Instructor
Joined: Feb 2015
Posts: 104
Likes: 0
From: Wichita KS
The '84 - '87's have limit switches inside the headlight motors that get dirty. Not a difficult job to clean them. There is lots of information on this procedure on this forum. Use the "search" function at the top of the page. Cliff Harris' write-ups on this problem are excellent.
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
What you might want to try is to swap the two larger relays and see if the problem goes to the other headlamp.
Part #'s:
Headlamp Relay AC Delco D1784 (GM 10031018)
Isolation Relay AC Delco 15-2386 (GM 10039961)
The isolation relay will be slightly smaller than the two headlamp relays.
Thread Starter
Instructor
Joined: Feb 2015
Posts: 104
Likes: 0
From: Wichita KS
The early C4's use 3 relays for the headlamp motors. One each (both are the same p/n's) for the left and right motors and an isolation relay. The isolation relay changes the current polarity at each motor so effectively when you shut off the headlamps, the motors run backwards. The fact that one headlamp works both directions probably means that the particular relay for the passenger side motor may be failing.
What you might want to try is to swap the two larger relays and see if the problem goes to the other headlamp.
Part #'s:
Headlamp Relay AC Delco D1784 (GM 10031018)
Isolation Relay AC Delco 15-2386 (GM 10039961)
The isolation relay will be slightly smaller than the two headlamp relays.
What you might want to try is to swap the two larger relays and see if the problem goes to the other headlamp.
Part #'s:
Headlamp Relay AC Delco D1784 (GM 10031018)
Isolation Relay AC Delco 15-2386 (GM 10039961)
The isolation relay will be slightly smaller than the two headlamp relays.
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