ammeter needle pegged
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Senior User
Joined: Jan 2003
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From: willamette valley ore
ammeter needle pegged
I've been away from the forum for a while and I missed it so here is my latest issue for you guys to help me with. When I pull the headlight switch in my '65 F250, the lights come on OK for a couple of seconds and then they go dim and then bright and keep alternating like that. When they go dim, the ammeter needle pegs to the discharge side and the gauge clicks. If I do not turn on the lights, the truck starts and runs fine with no fluctuation of the ammeter needle. Sound familiar to anyone? I replaced the headlight switch and then the regulator because I had good ones on the shelf but they did not make any difference. Thanks, Steve
Laughing Gas
Joined: Dec 2010
Posts: 1,091
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From: Tucson, Arizona
I could be entirely wrong, but what I think you're describing is a dead short in the headlight circuit (chaffed or trapped wire?) that is causing the circuit breaker built into your light switch to cycle. Short circuits will cause the amp meter to go to full discharge. Hope you find your problem.
Logistics Pro
Joined: Mar 2012
Posts: 4,389
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From: placer county usa?
I could be entirely wrong, but what I think you're describing is a dead short in the headlight circuit (chaffed or trapped wire?) that is causing the circuit breaker built into your light switch to cycle. Short circuits will cause the amp meter to go to full discharge. Hope you find your problem.
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More Turbo
Joined: Nov 2010
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From: NJ
Just curious...Do the lights dim if the engine is off? Is the vibration of the motor causing enough movement of the headlight wires to short to ground? Wiggle them with engine off. Do they dim then?
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Laughing Gas
Joined: Sep 2003
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From: Corbett, Oregon
I could be entirely wrong, but what I think you're describing is a dead short in the headlight circuit (chaffed or trapped wire?) that is causing the circuit breaker built into your light switch to cycle. Short circuits will cause the amp meter to go to full discharge. Hope you find your problem.
The problem appears to be in the headlight circuit. The pulsating of the lights is most likely the circuit breaker reacting to a short circuit or a fault to ground.
I would focus on the headlight circuit since you say the rest of the appears to work as normal.
Good luck.
Roger Carter
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