Engine shuts off when headlight switch is pulled out.
A friend of mine had an electrical problem show up in his 66 vette. When you pull the light switch out the engine quits running just like you turned the key off. It doesn't do it with just the parking lights on but if you turn on the turn signal with the parking lights on it cuts the engine out every time it blinks. If you shut the parking lights off and turn the turn signal on the engine runs fine. He has replaced the light switch but that didn't help his problem. I think it is opening a relay when you pull the light switch out that should remain closed. It doesn't blow any fuses when this happens and everything seems to run fine otherwise. Any thoughts on a starting point to track down this gremlin would be appreciated.
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Re: Engine shuts off when headlight switch is pulled out.
Hi David:
I am not an electrical expert but a good starting place is the wiring schematic --- you can get the color coded one from Doc Rebuild ---it has a clear depiction of the wires and colors ---and more importantly, the various connectors... you can trace the wires along from the AA and BB firewall connectors to the head lamp switch and directional signal flasher connection --- this should give you an idea of several places to look for possible problems... hope this helps or at least gets you going in the right direction.....
Regards
Bill -
Re: Engine shuts off when headlight switch is pulled out.
Many vintage car manuals used to say to adjust the curb idle with the headlights on and A/C on. Headlights DO add an add'l engine load.
The point being...maybe your pal's idle speed is just plain too low...
Unless your buddy has a power top or power windows I don't know of any relay that would be activated.Comment
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Re: Engine shuts off when headlight switch is pulled out.
I'd think there might be a fault in the wiring harness that allows a direct path to ground when the headlights are turned on. Shorts to ground are one step before a fire under the hood. Inspect the harness immediately and don't leave the car unattended with the battery connected.Comment
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Re: Engine shuts off when headlight switch is pulled out.
One more idea....was the distributor switched to pertronix or similar?
If they connected it to the resistor wire instead of running 12 volts, a draw from the.headlights could definitely cause thisChris
'72 Lt-1 a/c Pewter Silver coupe Mason Dixon Chapter Top Flight 2016
'73 L82 4 spd Dark Metallic Blue coupe Chapter Top Flight 2023Comment
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Re: Engine shuts off when headlight switch is pulled out.
The headlight switches have a thermal circuit breaker internally; excessive current will cause the headlights to 'strobe'...that would happen before the entire car shut down electrically I would think...Comment
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Re: Engine shuts off when headlight switch is pulled out.
I think so too. The short is so strong it's dropping the primary voltage so low that it's below the required voltage to generate spark. This also tells me that the battery condition may be marginal.
The CB inside the HL switch should trip, but if old and defective it may not trip, or maybe it trips late after the engine dies.
Certainly a weird problem though.Comment
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Re: Engine shuts off when headlight switch is pulled out.
What does a load test on the battery show?Judging Chairman Mid-Way USA (Kansas) ChapterComment
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Re: Engine shuts off when headlight switch is pulled out.
This shouldn't be hard to find. Pull the headlights switch on and let the eng stall. Now take your volt meter and follow the ign circuit back starting at the coil +. When you find your interruption in the ign circuit you will have found the correlation to the headlights as well.
It is a continuity issue. When there is a system draw high enough the connection is lost. That's why it does it with headlights and not park lights, but if you add turn signal to park lights it happens. When you follow the ign circuit back you will come to a point where the power is sourced for both ign and lights. Somewhere there or back is where the issue will be.
It's not a ground issue because the ign relies on eng block ground. The block ground is secure enough to handle 200 amps of starter draw, far more than the couple amps of light draw. Same with the battery.
It's not a dead short in the headlights because the circuit is protected with a circuit breaker. It will trip and reset in a short. If the circuit breaker were not working, stuck in on, it would have burnt the wiring by now.
SteveComment
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Re: Engine shuts off when headlight switch is pulled out.
Per Steve:
"When you follow the ign circuit back you will come to a point where the power is sourced for both ign and lights. Somewhere there or back is where the issue will be......"
Per the wiring diagram mentioned above --- The ignition harness connects to the "AA" 2x4 box on the firewall --
The head light harness connects to the "BB" 2x4 box on the firewall --- these two boxes are adjacent to one another ---just under the brake master cylinder ----
Some time back I had an issue with the engine in my '66 simply stoping --- no power ---nothing --- I pulled both the the main connectors to the "AA" and "BB" box off and found the lower connectors to be corroded --- this is an original 66 wiring harness in an unrestored car so the corrosion was long term ----it was not all messed up ---just a little white residue and some green oxidization but it was enough to cause the problem----
I cleaned up the contacts thoroughly and put the plugs back in --- no problems since ---- might be worth checking those two 2x4 plugs for corrosion ---- "everything" passes through those two grids between the interior and the engine compartment.... just a thought.
Regards
BillComment
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Re: Engine shuts off when headlight switch is pulled out.
Bill,
Won't hurt to check it, but the two circuits are running parallel at the point they pass through the firewall. Poor connection on one or both at that point won't cause a fault in the circuit beside it. Would have to be a point prior to power splitting off to the two circuits.
If I were a betting man my money would be on the terminal on the main power feed wire where it connects to the batt terminal on the solenoid.
SteveComment
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Re: Engine shuts off when headlight switch is pulled out.
Guy's thanks for all the help. Yesterday I traced the circuits with a volt meter and couldn't find anything. Out of desperation we tried his old voltage regulator, when we was taking the one off the car we found a large wad of lint and steel wool fibers from when he was cleaning on the car stuck under the regulator against the resistor on the bottom. We plugged the old regulator in and the problem went away. Cleaned up the back of the new regulator and put it back on and car is working just fine. He drove the car pulling the light switch on and off all day and into the night without one bit of trouble. Don't know if that was the true fix but for now the car is problem free, if anything changes I'll repost.Comment
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Re: Engine shuts off when headlight switch is pulled out.
Steve--
I wondered about that given that the diagram does clearly state that the lights are in one and the ignition harness in the other ----
I would agree the main power feed is also a good suspect in this case!!!
Later
BillComment
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Re: Engine shuts off when headlight switch is pulled out.
Excellent!!!!Comment
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Re: Engine shuts off when headlight switch is pulled out.
I hate when that happens, where the problem disappears without first finding the definitive answer. The shorting of the resistor on the bottom of the reg has a low probability of being the cause. More likely that would show up in inconsistent charging. While connected to the main feed, it's connection is fairly remote.
What always troubles me when I don't find the absolute answer is that it will show up again when I least want it.
SteveComment
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