Bright Lights kill the engine
Thread Starter
3rd Gear
Joined: Mar 2014
Posts: 3
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Bright Lights kill the engine
My 1978 Vette has started having an issue where if I turn on my bright headlights, it kills the engine. Has anyone else ever had this issue? I have been wanting to upgrade my headlights to the newer brighter headlights, not sure if this will fix the issue, or if I need to try and fix the issue first. Any help is greatly appreciated.
Race Director
Joined: Nov 2006
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From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
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Cruise-In VIII Veteran
I'm thinking you better fix the issue first. Then once the problem is sorted. Add headlight relays and then your new brighter headlights.
2026 Loser of the Year
Joined: Sep 2013
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From: New Or-leens Loo-z-anna
Do NOT start the engine:
Hold the headlight wire that comes through the firewall BEFORE you turn on the lights.
Is the wire warm or room temperature?
Turn the headlights on LOW BEAM.
Is the wire warm or hot after a couple minutes?
Turn the HIGH BEAMS on.
Is the wire warm, hot, or very hot?
START the engine and repeat the above tests.
Let us know the answers.
Hold the headlight wire that comes through the firewall BEFORE you turn on the lights.
Is the wire warm or room temperature?
Turn the headlights on LOW BEAM.
Is the wire warm or hot after a couple minutes?
Turn the HIGH BEAMS on.
Is the wire warm, hot, or very hot?
START the engine and repeat the above tests.
Let us know the answers.
Race Director
Joined: Apr 2011
Posts: 11,183
Likes: 3,334
From: North of Toronto - Ontario
WAG, Check the connections to the distributor coil / module. If you have another one laying around try swapping them. It's possible the highbeams are drawing that extra bit of juice to pull the coil/module down too low.
M
M
Melting Slicks
Joined: Jul 2005
Posts: 2,649
Likes: 863
Start the car - and check voltage from coil pos to ground:
1) With no electrical accessories on.
2) With parking lights only
3) With Low Beams only
4) With High Beams.
Let us know ...
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From: New Or-leens Loo-z-anna
It could be a single problem,or several problems.
As the members said...weak alternator...corroded-loose connections..hi amperage radio-speakers...high amperage cooling fans...etc.
You wouldn't be using the HEI 12V wire to supply current to anything else...
would you?
As the members said...weak alternator...corroded-loose connections..hi amperage radio-speakers...high amperage cooling fans...etc.
You wouldn't be using the HEI 12V wire to supply current to anything else...
would you?
Race Director
Joined: Nov 2006
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From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
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Cruise-In VIII Veteran
All good points above. Although the holding the wire in your hand idea may be difficult compared to just testing voltage.
what does your volt gauge on your dash read when idling? It should be 14.5 volts. Or very close to that.
Does the volt meter on the dash drop when you turn on your lights?
It shouldn't.
what does your volt gauge on your dash read when idling? It should be 14.5 volts. Or very close to that.
Does the volt meter on the dash drop when you turn on your lights?
It shouldn't.
Race Director
Joined: Mar 2017
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From: Virginia
What is your voltmeter doing when this happens? One night, I noticed that mine would drop to 11.5V, and slowly decrease, as the high beams drained the battery. I drove home on low beams, and upgraded to a 150A 3-wire alternator. That fixed my problem, but some more info would help for yours.
@interpon has a thread showing how to rebuild an alternator, which is also a warning on buying rebuilt alternators.
@interpon has a thread showing how to rebuild an alternator, which is also a warning on buying rebuilt alternators.
Le Mans Master
Joined: Jun 2019
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From: Indiana
What is your voltmeter doing when this happens? One night, I noticed that mine would drop to 11.5V, and slowly decrease, as the high beams drained the battery. I drove home on low beams, and upgraded to a 150A 3-wire alternator. That fixed my problem, but some more info would help for yours.
@interpon has a thread showing how to rebuild an alternator, which is also a warning on buying rebuilt alternators.
@interpon has a thread showing how to rebuild an alternator, which is also a warning on buying rebuilt alternators.
about post 114 give or take.