I'm a fair mechanic and could use some ideas before I bloody my knuckles. The battery in my '89 vert drains down over night. I've got a FSM and am pretty good with low voltage, so where would you start? Got good grounds, so I suspect a relay is staying closed after shutdown. Voltage regulator? What do you say?

Dave

 

What I have done in the past is hookup a volt meter to the battery to watch the voltage drop. Then I start pulling 1 fuse at time (remove and replace one at a time). To watch the voltage drop.

That should give you an idea where the voltage drain is....

 

That works, but also depends on the current draw, so you might not see it by measuring just voltage.

I would recommend reading current instead, most voltmeters support this. To read current though you need to break into the circuit by putting your meter between the negative lead and negative battery post. What I did when I was troubleshooting a current draw was to get a long speaker wire (2-wires) and attached alligator clips on each wire. That way I could have my voltmeter in the car while pulling the fuses to see the draw either stay or go away.

I was having a similar problem and was seeing 2amps being pulled with everything off...for my 96 it should be more like .03amps. Turn out my Real-Time Dampening module was shot and a bad voltage regulator had gone bad in a shorted state.

Also you really need to be careful when something is causing your battery to be dead everyday. This means current is being pulled somewhere and that device is heating up...depending on where the device is, it could get hot enough to cause a fire.

Until you find the current draw, I suggest disconnecting the battery when possible. Something draining the battery overnight means it's drawing a decent amount of current.

Not sure about an 89, but I also had fuses under the hood too by the battery, so don't forget about those if you have them there too in your model year.

BTW...you have confirmed that you don't have a bad battery?

 

Thanks for that hint. It's just what I needed. The battery was replaced in '09 and has worked fine until now. I took it out first and it checked O.K. after it was recharged. I'll rig up my digital meter and see what it shows. That should save a lot of hunting and scraped hands.