Needle on ammeter shows slight charge when engine is started and works fine until brake pedal is depressed. The needle deflects completely to the left when the pedal is depressed, then returns to normal once the pedal is released. Any thoughts are appreciated.
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Re: Bouncing Ammeter Needle
Sounds like a possible short circuit somewhere in the stop light circuit, but not enough to blow the fuse. With a voltmeter attached to the battery and the engine idling, the voltage should be above battery voltage - say 13.5. Step on the brake and observe the voltage. If it drops below about 12.5 there is a big current drain - so much that the alternator cannot supply enough current to maintain normal system voltage, and the first place to look is the stop light circuit.
The ammeter is really a voltmeter that uses the slight difference in voltage between two points in the wiring as a surrogate for whether the battery is discharging or charging, and they sometimes give odd readings. That's probably why the industry finally abandoned them in favor of just plain old voltmeters that directly read system voltage.
Duke -
Re: Bouncing Ammeter Needle
does the needle move before the brake lights come on? if so, it sounds like a rubbed jacket in the area of the pedal arcing to the chassis. if not, it's a short somewhere in the harness. the fuse should blow, though. I would disconnect the battery everytime you leave the car.
shorts in vettes = fire. check the resistance in that portion of the circuit and see what the number is. it should be negligable.
EdComment
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