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1978 corvette headlight relay

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Old 04-20-2011, 09:35 PM   #1
1974rag
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Default 1978 corvette headlight relay

I have a 78 Silver Anniversary and am almost complete a full update. We have determined that the headlight relay has become corroded and is preventing the headlights from turning on. The problem is that GM has discontinued this relay GM part# 5627362.

Does anyone know where I can buy one new? or is there a fix anyone can recommend?

Thanks for your help
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Old 04-20-2011, 10:11 PM   #2
Oldguard 7
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Which relay left or right. If I'm right there are two. Must the part be an original? If so maybe one of the corvette salvage yards may have them. I like Contemporary Corvette, then J&D Corvette. If not all of the corvette vendors sell them. The actuators open them, the relays close them.
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Old 04-21-2011, 09:24 AM   #3
Crash80
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Quote:
Originally Posted by 1974rag View Post
Does anyone know where I can buy one new? or is there a fix anyone can recommend?
Willcox had everything I needed when I attacked this issue on my 80. They have a helpful section with write ups on how to do lots of stuff on Vettes too....
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Old 04-21-2011, 09:50 AM   #4
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Just about every vendor has them.
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Old 04-21-2011, 10:01 AM   #5
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Quote:
Originally Posted by 1974rag View Post
I have a 78 Silver Anniversary and am almost complete a full update. We have determined that the headlight relay has become corroded and is preventing the headlights from turning on. The problem is that GM has discontinued this relay GM part# 5627362.

Does anyone know where I can buy one new? or is there a fix anyone can recommend?

Thanks for your help
When you talk about a corroded relay, it sounds like you are referring to an electrical part. I may be wrong, but I don't know of any electrical relay in the 78 headlight system, and I haven't been able to find that part number in my GM books.

Do you have a GM group number for the relay. Where is the relay your looking for located.

There are 2 vacuum relays, one for each headlight. They're mounted to the front surround panel reinforcement. They open and close the headlights, by controlling the vacuum to each headlight. The GM part number for these was 5638427. They are discontinued now, but repros are available for about $60 from most Corvette vendors.
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Old 04-21-2011, 11:56 AM   #6
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Stock '78s do not have electrical headlight relays. The little foam filters in the headlight vacuum system relays can deteriorate and/or fall out. They will then ingest crud that can look and act like corrosion and prevent the "dog bone" valve from sliding and properly directing vacuum to the headlight vacuum actuators.

First, check the integrity of the diaphragm in the top (disk-shaped end) of the relay by attaching a vacuum pump to the SMALL port extending from the metal "hat". If it does not hold a vacuum, the diaphragm is bad and the relay cannot be repaired. If it does hold vacuum and the crud or corrosion is preventing the "dog bone" valve from sliding and correctly porting vacuum to the actuators, repairs may be possible.

Before disassembling the relay, you might try squirting WD-40 into the 3 LARGE vacuum ports and into the bottom end of the relay after removing the filter material, if any. This has been successful for some in freeing up the "dog bone".

My sticky thread, "How Your Headlight Vacuum System Works" includes info and links to more easy relay tests (and other headlight vacuum system tests) you can perform and links to a couple of fairly easy "dog bone" valve repairs that have been reliable and saved some $$$.

Good luck!
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    1978, 78, actuator, c3, corvette, filter, headlamp, headlight, headlights, location, opening, override, parts, relay, troubleshooting, vacuum, valve, vette, wilcox

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