Headlights not working, all other lights do
Thread Starter
1st Gear
Joined: Oct 2007
Posts: 1
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Headlights not working, all other lights do
New to the forum, hope someone can help.
Trying to determine why the headlights on my '78 Vette don't work. Every other electrical device is operable, but no the headlights. I've changed the light and dimmer switches, as well as the headlight bulbs, but still no lights. There is no fuse. The owners manual states there is a circuit breaker within the light switch which will cause the headlights not to function, due to an overload on the circuit. Nothing has changed on that circuit, so I don't know what the overload could be.
I've checked the wiring diagram and the only grounds in the circuit are also used by circuits that are functioning.
Thanks for any guidance,
Paul
Trying to determine why the headlights on my '78 Vette don't work. Every other electrical device is operable, but no the headlights. I've changed the light and dimmer switches, as well as the headlight bulbs, but still no lights. There is no fuse. The owners manual states there is a circuit breaker within the light switch which will cause the headlights not to function, due to an overload on the circuit. Nothing has changed on that circuit, so I don't know what the overload could be.
I've checked the wiring diagram and the only grounds in the circuit are also used by circuits that are functioning.
Thanks for any guidance,
Paul
Racer
Joined: Sep 2005
Posts: 359
Likes: 0
From: Shoemakersville Pa
New to the forum, hope someone can help.
Trying to determine why the headlights on my '78 Vette don't work. Every other electrical device is operable, but no the headlights. I've changed the light and dimmer switches, as well as the headlight bulbs, but still no lights. There is no fuse. The owners manual states there is a circuit breaker within the light switch which will cause the headlights not to function, due to an overload on the circuit. Nothing has changed on that circuit, so I don't know what the overload could be.
I've checked the wiring diagram and the only grounds in the circuit are also used by circuits that are functioning.
Thanks for any guidance,
Paul
Trying to determine why the headlights on my '78 Vette don't work. Every other electrical device is operable, but no the headlights. I've changed the light and dimmer switches, as well as the headlight bulbs, but still no lights. There is no fuse. The owners manual states there is a circuit breaker within the light switch which will cause the headlights not to function, due to an overload on the circuit. Nothing has changed on that circuit, so I don't know what the overload could be.
I've checked the wiring diagram and the only grounds in the circuit are also used by circuits that are functioning.
Thanks for any guidance,
Paul
Did you try bypassing the cicuit breaker with a jumper wire just to make sure the circuit breakers not the problem?
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,114
From: Crossville TN
Is there not a headlamp relay in that model year car? [could be only a circuit breaker...then that would be the likely cause...] It also could be a damaged ground circuit to the lights...if the bulbs are the only electrical item on that circuit. Pull the bulb on one of the lo-beam bulbs and use your volt-ohmeter to check for 12v at the socket (for both hi & low beam supply). If no voltage at the bulb socket, it has to be in the wiring/supply circuit system. If you do have voltage, the ground circuit is bad...or your bulbs are blown. You might as well check the bulbs for resistance continuity across the filaments, too.
Last edited by 7T1vette; Jul 20, 2009 at 01:55 PM.
Advanced
Joined: Nov 2006
Posts: 64
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Don´t know exactly how the 78 system works. On my 82 the +12V is coming from the starter motor, goes up the engine and there is the first connector close to #8 cylinder on the valve cover (here I once had a problem with the connection). Then it goes through the firewall to the light switch. Here you should measure the 12V. If the power is not there then you should follow the line "upstream" to the supply until reaching the battery. Somewhere is a break then.
If you have the 12V power on the switch you can measure the power is going through the switch when selecting lights on, then the switch is good. Just follow the wire to the lights and measure the 12V whereever you can, you should be able to find the break then. Hope this helps. Good luck.
If you have the 12V power on the switch you can measure the power is going through the switch when selecting lights on, then the switch is good. Just follow the wire to the lights and measure the 12V whereever you can, you should be able to find the break then. Hope this helps. Good luck.
Melting Slicks
Joined: Feb 2007
Posts: 2,707
Likes: 268
From: S.E. MI
St. Jude Donor '15
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,114
From: Crossville TN
There's a circuit breaker on or inside of the light switch [on the dash]; that's most likely the problem. Other possibilities are the power feed line going to the light switch, feed line coming out of the light switch {check both of these with your multimeter to exclude them}, headlight ground wire which goes to the alternator ground lug, and any fusible links that are isolated to the headlight circuit.
If you determine that the switch circuit breaker is 'blown', you need to determine "why" before you replace/reset it and try it again. Chase down the lines for continuity between power line and ground with battery disconnected but circuit breaker repaired. The light switch itself may have failed and cause a dead short.
If you determine that the switch circuit breaker is 'blown', you need to determine "why" before you replace/reset it and try it again. Chase down the lines for continuity between power line and ground with battery disconnected but circuit breaker repaired. The light switch itself may have failed and cause a dead short.
Last edited by 7T1vette; Jul 21, 2009 at 09:58 AM.
