Originally Posted by jfb

You have high leakage current discharging your battery. GM says leakage current (battery current drawn with everything off) should not exceed 50 milliamps. My 87 draws 27 ma. and I have no battery problems. First, don't leave your key in the ignition as this keeps the theft alarm circuit on. Next, at night, in the dark, see if your underhood lights are on, vanity mirror lights, center console lights, door map lights, spare tire lights, courtesy lights. Do you have a radar detector, GPS, CB transceiver, aftermarket radio or audio amplifier? Check em.
Next, buy a VOM test meter (voltmeter, ohmeter, milliameter). You can buy one at Harbor Freight for $7 and its a pretty decent meter too!
Pull your courtesy light fuse, then disconnect the negative battery terminal and connect the VOM set up to measure current and connect the test probes from the battery post to the battery cable so you can measure current. It should be less than 50 milliamps. My bet it is much higher, then start removing fuses one at a time and watch the ammeter. If you see a dramatic drop, then that fuse circuit will need to be investigated. Seat motor switches sometimes are the culprit, keeping a seat adjust motor on. Feel seat motors, if warm, then this could be the problem. Also, remove the nut on the bolt behind the battery with 8 red wires connected. Remove the wires one at a time while watching the ammeter. Again, a sudden drop in current indicates the problem and you will have to follow that red wire to see what circuit it is.
Lead acid batteries don't like sitting for long periods (4+ wks). They self discharge even disconnected and while dead, the battery plates become sulfated and they will not take a charge and you have a door stop! If you park your car for a long time and you don't have high leakage current, then buy a battery tender and connect it to the battery. Tenders continually measure the battery voltage and charge the battery if its state of charge falls 10% and then shut off. This keeps your battery up and it will experience a normal life. Battery tenders may not be able to supply high leakage current and some tenders will indicate that you have excess leakage current.
Putting a battery disconnect switch on your battery doesn't solve the root of your problem, it hides it, and also, you will lose your radio station presets and miles driven info. Forget the battery switch and find the problem.
I'm surprised the dealer who told you the seat switch was stuck didn't replace the switch!

Originally Posted by JrRifleCoach

Zeeman

Look into the headlight well(s). There are three connectors per side that lead up to the hood.

The two pin connector is for the underhood lights.

Originally Posted by 87Vetteowner

I had a more or less consistent battery drain on my 87. One day, when it was extremely quite out, no birds chirping, no background car noise. I found the drain on my car. It was the door lock system. Mine was clicking on and off, making a very faint clicking sound. Once I fixed that. mine went away.

There are a lot of things that go go wrong. Usually it isnt the charging system in a C4, it seems to be a bad switch or ground.