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69tr

Jedi Trainee
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The amp gauge on my car will sometimes fall to negative for a short period. I checked the voltage when it does this and it is only about 11.5 volts. I think it has the original alternator. Has any one else had this problem?

I checked the belt and it is tight. It does this if I have something on (lights etc) and with everything off.
 
69tr, check your ground strap, it should run from the batt to fire wall to rear of engine. A short strap from the engine block at the motor mount, (one of the 4 bolts), to the frame is good insurance. If all is there, take apart and clean paint away to make good contact. Hope it's that simple. Wayne
 
IMO, if the voltage is going that low in a short amount of time, you have a substantial short somewhere. If it was just the alternator not working for some reason, the battery voltage should only drop to about 12.6 for at least an hour or so.

Could be a bad battery, though, so to double-check: Try turning on the headlights with the engine off and checking the battery voltage.
 
I believe that the ground strap in intact but I will check it.

I will also check the battery voltage with the lights on.

The voltage only drops to about 11.5 volts. It doesn't seem like a short. Could it be the voltage regulator?

Thanks
 
How far negative does the ammeter go, when the problem happens with the headlights off?

The regulator cannot tell the alternator to consume power; the worst it can do is disable the alternator. Normally, that would cause the battery voltage to drop fairly quickly to 12.6; and the entire electrical load to appear on the ammeter as a discharge. Without the headlights (heater, etc.) that load should be only a few amps (less than 5), so only a tiny deflection on the ammeter. If you're getting a big deflection, something is taking current that shouldn't be (like a short).

And for a healthy, fully charged battery to drop that low; something is taking major current out of it. Normally, with only a 5 amp load, the voltage wouldn't drop that low until the battery was mostly discharged (under 20% charge remaining).
 
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