Parasitic battery drain. Help!

One of the first things to check: Do all interior lights work exactly as designed?

All of the lights have a three-position switch - OFF, ON, AUTO. With the switch in AUTO, the light must come on when a door or the hatch is open, go off when it is shut. If the interior lights do not work like that, start with the hatch switch, then the door switches, then a shorted wire in the light near the interior mirror.

Check the glovebox light and under-hood light.

Thankyou Wally. Will do. I'll post the result of my efforts in a week or two as I monitor the battery. I'm going to make one change at a time to see if the problem can be isolated. The drain can only be measured at .5mA. Is that in the realm of "normal"? I thought the clock and maybe computer memory would draw that much? The battery is stone dead in a week or two of "sitting" and that's what led me to think something was turning on itself on while the car was idle?

I think that you have slipped a decimal point - the "normal, expected" drain on a late model 928 is 20 mA. A reading of 0.5 mA (0.005 Amp) is virtually unmeasurable. If the measurement is actually 50 mA, that is high, but the battery will last one or two weeks. If the measurement is actually 0.5 Amps, the battery will last one or two days.

Thanks Wally,
You must be correct. It must be 50mA. The battery is definately dead in one or two weeks not one or two days. This past Thursday it was 12.20 V and today (Sat.) it's 12.06 V. I pulled the rear defroster relay on Thursday. If the drain is 50mA would pulling the fuses one at a time enable me to diagnose the source of the drain?
Thanks again, Bill

Bill, that's the idea. usually, when you pull the offending circuit's fuse or relay, you should see a drop in the amp meter. that would give you a good idea of where to look.

After extensive searching, I finally found that a similar drain on my '90 GT was due to a faulty SCR in the fan amp on the panel forward of the radiator. Only easy check is to unplug the amp and see if the current draw goes down. Remove one screw, pull the plug.