Battery drain on 91 Coupe. need help badly.

[RegalMan]

Hello, i'm new here. i am having some serious issues with my 91 Buick Regal Coupe. it has drained 3 batteries and is working on the 4th as we speak.

we have replaced the alternator already, and my mechanic has checked everything he knows to check. we thought it may have been as simple as a censor or a loose wire. i kind of suspect that he hasnt checked everything, so i am hoping someone here can help before i spend the money i really cant afford to spend on another one.

for now i just disconnect the battery when i get out. this is getting to be a real hassle... any help will be appreciated.

[raybuick]

Hey Regalman, Some simple things to check for are like a light being left on, like in the trunk or under the hood from a bad switch. If you have powerlocks, take the fuse out for them and see if the charge holds.I had this problem and a short would drain the battery completely dead overnite. Good luck and let us know how it turns out.

[Mr_D]

If you haven't already done so, you could try the following:

Install a DC amp meter inline with your positive battery cable and read the current draw while all systems are off. It should be at 20mA DC or below. If it says ~100mA, no big deal, that's out of spec but it should be able to run that amount for a week or more. mA means milli amp.
1 amp = 1000mA.
Just for scale, parking lights typically draw 5 to 10 amps, about the same as the radio.

Here's how: Disconnect the + battery cable, run the 12V power from the battery + terminal through the meter, and back out to the + 12V cable you just removed. Bascially the battery is connected again just like it was, except it runs through the meter. Careful not to turn on anything or you could melt the meter or at least blow a fuse. The meter should be able to handle brake lights and so forth but limit it to a couple seconds if it reads over 10 amps.

(To be safer, disconnect the negative battery cable instead and use a digital multimeter that doens't care about polarity. If it says - (negative) currrent just switch the meter leads around.

Turn off everything, headlights, heater fan, radio, dome light, close the doors, etc. I use a standard Fluke 83 multimeter for this which handles 15 amps DC max. Careful about the dome light coming on too. Could be 5 amps, could be 15. depends on your car.

With everything off, the current draw should be below 20mA. That is the GM spec for a 98 Buick and other models should be very similair. That's just enough to run the clock. The current may be higher initially until various timers (if present) time out. If you wait 10 minutes and you still read a few hundred mA or worse yet, even a few Amps, then you do have a leak. GM calls this a Parasitic load.

Then remove all the fuses in the vehicle one at a time and watch the current meter. If it drops while pulling a certain fuse you've narrowed it down to a specific circuit. If the current stays high, also disconnect the alternator wires, and the various relays noting their original positions. Most likely, it's the wiring in a circuit somewhere that rubbed through the insulation or a relay or module with a short. Pulling the fuses will show you which circuit has the problem. Have someone who knows electronics help connect the meter if you have any questions. Good Luck.