Got my '92 going again and have a voltage drain. The PO straight wired the cooling fan and has a toggle switch, need to figure out why he bypassed the original system. Charges good until you flip the toggle, the amp meter reads less than half. Drove less than 10 miles on a fully charged battery, once at night and headlights were very dim. Next morning battery was totally dead. Battery is 11 month old Wal-Mart special, think I'm going to take it back to eliminate that. Had changed alternators with a good used one before my transmission problems, thread lost, and was working good I thought but without any night time driving using cooling fan, defroster, and headlights. Any ideas or thought processes on determining the problem will be greatly appreciated. Got money tied up in this Stang and would like to enjoy it before my new tires dry rot. kennyg

 

A bad voltage regulator could be the cause. If I remember correctly, they put it into the alternator, but it it is serviceable. It's that , or the diode plate in the alternator. Either way, to me it sounds like the charging system can't keep up with the drain of power. If the battery will take a charge and survive a dummy load test, I would check the alternator, and all the wires leading up to the alternator for missing insulation or bare touching (shorting) wires. A good place to look is where the wires pass through the firewall. Check the charging harness closely! If the wires are bare and touching each other in the alternator harness, when you shut the car off, the alternator fields will remain energized, which slowly drains the battery over a 4 - 6 hour period. Been there, seen that!

 

Take it to a place like Auto Zone or Advance Auto. They will test your charging system, free.

 

Put my battery on charge today. Started with 0.00 volts. After 4 hours on a 2 amp charge, then sitting to equalize, 5.30 volts. Will charge more tomorrow, but found my Wal-Mart receipt from 12/19/08 with a 1 year no cost exchange. I'm betting I take this one back. kennyg

 

I would definitely exchange it for another one while you still can...obviously, it wouldn't hurt to have a fresh battery after you find the problem in your electrical system...I just did it with my Optima red top.

 

Charged my battery on 2 amps again yesterday for 6 hours. Got it up to 5.80 after equalizing. Did the Thanksgiving thing today with family but did stop by Wal-Mart and exchange the battery. They hooked it up to their load tester and it read 4.04. They gladly exchanged it. Finally I may get to mess with it tomorrow and take it for a drive. kennyg

 

Took the Stang for a drive today. Hooked the battery up and there is a very slight power usage detected when I hooked up the battery. The underhood light had already been pulled and I took out the trunk light bulb to eliminate the possibility that it might be staying on when closed. While driving, about an hour before sundown, I was forced to use the sunvisors. The mirror cover flopped down on the drivers side and the passenger mirror cover was missing, only the fabric was there. The lights came on for both the vanity mirrors. My wife could mess with the switch and get the right to turn off, and if the left was closed carefully, it turned off. Maybe this is what has been causing my battery to run down, and besides the fact that it was defective. I'm driving it into work tomorrow for a half day of work and will get home before dark and won't have to use the headlights so I can see how the daytime systems work. kennyg