86 mustang gt is over charging,and any battery goes dead over night,i disconnect at night now,in morning hook back up and starts up,could it be voltage regulator?


Asked by Feb 04, 2012 at 07:08 AM about the 1986 Ford Mustang GT

Question type: General

battery bubbles,voltometer is half way when just running,lights arent dim,

5 Answers


IIRC, the voltage regulator is built into the alternator. So, replace the alternator. ;-)

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It also sounds like you have a short to ground. The way you describe it in the question it sounds like this is a 'live short' which means that when the ignition is OFF something is still drawing power and it kills your battery. Finding a live short is not easy as there is no way to know what circuit it is on. It is not on a switched circuit as a switched circuit is only in play whem the igniition is turned to the 'ON' or 'ACC'. To find this requires a lot of patience, knowledge of DC (Direct Current) cicuitry, and close visual inspection. It may be that the previous owner wired the stereo to a live circuit and the circuit is always drawing power. Look first for any circuit repairs or places where the circuit has been spliced into. Then look for exposed wires. Next look at the wires going into the door. Next look at the back of the fuse block. It could be on the interior light circuit, or the headlight/taillight circuits, or the cigarette lighter circuit. Grab a voltmeter and start testing. The voltage regulator is like David said, in the alternator. But this would only affect charging the battery while driving. Unknown (i.e. overnight) battery drains are usually live circuit shorts.

2 of 2 people found this helpful.
Best Answer Mark helpful

short to ground sounds best

2 of 2 people found this helpful.

CHANGE altenator it was drawing current when car was off,with old altenator i would touch post to battery and would make spark sound,new one touch post to battery and no sound.Does this sound right?


Short to ground can happen in an alternator. Usually as shorted alternator will not charge a battery while running. It is rare as it means the diodes and stators still work, but some wiring is shorted to the case of the alternator. If you do not get a draw (aka sparks at post) when the alternator is out of circuit this indicates the alternator is the cause of the draw. At this point check the wiring to/from the alternator. If all is good you may want to consider swapping to a higher amperage alternator. I like having a 130 Amp versus the original 75 Amp. I converted my '89 to use the '3G' 130A alternator from the 4.6L mustangs. Only changes are shaving a bracket back a little bit, the pigtail, and routing a heavier gauge wire back to the battery. Definately helps when you are running lights, windshield wipers, and radio at the same time. No more dimming at traffic lights in the rain.

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