Have a 86 firebird. Thought I had the battery drain fixed, HA. Wrong! Someone put in an after market radio, unhooked it. Still drained. Got a new radiator fan. Still draining. It'll last for about 2 to 3 days. Then dead as a door nail. Pulled every bulb inside, checked every fuse. New alternator, had it checked by 2 different shops. All good there. Im beyond my wits at this point! What else could be drawing the battery that fast?

 

 

Have you load-tested the battery?

If so, and it checks out OK, get a DVOM and follow ETCG's tutorial in the vid in post #2. A systematic search, using the factory wiring diagram for your car, will turn up the problem.

 

I have a 89 z28 with the same problem.Fond out the rear trunk lock was draining the battery. only fix i did was put a trickle charger on it when i put it up for storage.

 

Make sure the gray wire going to the radio isn't grounded.