new member from Ohio
Thread Starter
5th Gear
Joined: Jul 2009
Posts: 5
Likes: 0
From: cleveland ohio
new member from Ohio
Hi guys , just joined in hoping to learn a little about my new project. I have a 78 Silver anniversary. Im hoping to get the headlights to work in the next week or so. They wont open. I understand that if they fail they fail open. Is that correct? Dennis
Le Mans Master
Joined: Oct 2006
Posts: 6,388
Likes: 2
From: Eagle River Alaska
Welcome to the forum!
The headlights operate on a fairly complex vacuum system. I don't have the expertise to help, but someone here will.
Again, welcome.
The headlights operate on a fairly complex vacuum system. I don't have the expertise to help, but someone here will.
Again, welcome.
Last edited by Arcticshark; Jul 24, 2009 at 08:48 AM.
Safety Car
Joined: Aug 2001
Posts: 4,883
Likes: 11
From: North Easton Mass
Look up posts by Willcox Corvette. He recently posted vacuum diagrams that will help you troubleshoot the problem. There could be a few reasons why the headlights won't raise but you can start by finding out if all of the hoses are connected properly.
Rick B.
Rick B.
Drifting
Joined: Apr 2009
Posts: 1,345
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From: Melbourne Australia
Burning Brakes
Joined: Jan 2007
Posts: 1,164
Likes: 1
From: Port Clinton Ohio
St. Jude Donor '08-'09-'10-'11-'12-'13
Welcome from a fellow Ohioian.
My first Vette was a '76. The headlights didn't work. Turns out the brackets that held them in place were very rusty and some of them had broken.
Most of the time, headlight problems are caused by vacuum leaks. It is pretty common for the actuators behind the front bumper to go bad. From what I understand, they are very easy to rebuild. I would start the car and listen very closely for vacuum leaks. Repair any leaks that you find and then listen again.
Good Luck.
My first Vette was a '76. The headlights didn't work. Turns out the brackets that held them in place were very rusty and some of them had broken.
Most of the time, headlight problems are caused by vacuum leaks. It is pretty common for the actuators behind the front bumper to go bad. From what I understand, they are very easy to rebuild. I would start the car and listen very closely for vacuum leaks. Repair any leaks that you find and then listen again.
Good Luck.
Team Owner
Joined: Jun 2000
Posts: 38,923
Likes: 1,482
From: Southbound
Cruise-In II Veteran
Correct for half the time. The other half of the time, they fail closed. 
Operation of the headlight doors (opening and closing) is by vacuum. Operation of the headlights (on and off) is electrical.
Purchase a reproduction owner's manual for your '78. If you have an original manual, take it out of the car and store it in a safe place. Keep the repro in the car.
Purchase the assembly instruction manual (AIM) for '78. Lots of useful information in the AIM, including the color codes and routing for the headlight vacuum system.
Purchase the GM Shop manual for '78 if you intend to do most of your own work.
Operation of the headlight doors (opening and closing) is by vacuum. Operation of the headlights (on and off) is electrical.
Purchase a reproduction owner's manual for your '78. If you have an original manual, take it out of the car and store it in a safe place. Keep the repro in the car.
Purchase the assembly instruction manual (AIM) for '78. Lots of useful information in the AIM, including the color codes and routing for the headlight vacuum system.
Purchase the GM Shop manual for '78 if you intend to do most of your own work.
Last edited by Easy Mike; Jul 23, 2009 at 09:58 AM.
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Melting Slicks
Joined: Mar 2008
Posts: 2,023
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From: Austin Tx
I'm guessing that the lights turn on, but they don't pop up?
If they don't pop up, but you can raise them manually, then it's most likely a problem with the vacuum system somewhere.
Wilcox just recently created an awsome diagram, here's a link to it - http://willcoxcorvette.com/instructi...al_secured.pdf
If they don't pop up, but you can raise them manually, then it's most likely a problem with the vacuum system somewhere.
Wilcox just recently created an awsome diagram, here's a link to it - http://willcoxcorvette.com/instructi...al_secured.pdf
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
68 Welcome to the forum!
The headlamp vacuum system works in this manner.
In the diagram on my site, vacuum comes from the engine on two sides. One is the operations side (large hoses), one is the control side (small hoses).
When you pull the headlamp switch open it, at the same time it blocks the vacuum on the blue hose running from the headlamp switch to the over-ride and the entire system. Basically the small hoses control the relays that make the switch from up to down.
I’m working on a diagnostic page for all the systems but it will be a while before I have it done.
For now, I want you to go to the front of the car and with the car running pull off the black hose with the white stripe before it T’s into the two relays. The relay is the small valve with the silver top and the black body. See them?
Check to see if you have vacuum on this hose with the car running and without pulling the headlamps on. You should have vacuum at this point.
If you do have vacuum, use a set of needle nose pliers and pinch the hose closed with it installed on the car. This should make the headlamps come up.
Did it work? If not post back.
EasyMike. . . no offense and I'm sure you don't know this but that diagram is wrong. The source vacuum to the headlamp switch goes to the rear tit on the switch. Like shown below.
Willcox Inc.
The headlamp vacuum system works in this manner.
In the diagram on my site, vacuum comes from the engine on two sides. One is the operations side (large hoses), one is the control side (small hoses).
When you pull the headlamp switch open it, at the same time it blocks the vacuum on the blue hose running from the headlamp switch to the over-ride and the entire system. Basically the small hoses control the relays that make the switch from up to down.
I’m working on a diagnostic page for all the systems but it will be a while before I have it done.
For now, I want you to go to the front of the car and with the car running pull off the black hose with the white stripe before it T’s into the two relays. The relay is the small valve with the silver top and the black body. See them?
Check to see if you have vacuum on this hose with the car running and without pulling the headlamps on. You should have vacuum at this point.
If you do have vacuum, use a set of needle nose pliers and pinch the hose closed with it installed on the car. This should make the headlamps come up.
Did it work? If not post back.
EasyMike. . . no offense and I'm sure you don't know this but that diagram is wrong. The source vacuum to the headlamp switch goes to the rear tit on the switch. Like shown below.
Willcox Inc.
Last edited by Willcox Corvette; Jul 23, 2009 at 10:44 PM.
