1988 928 battery drain over night.

Just bought this 1988 928 everything works great except for the battery drain over night, even after a full charge. The car has a new battery and alternator and I see nothing visually that might be left on that could drain the battery. Only thing I see is when driving the car the alternator gauge never gets over 12 amps.
Any ideas ?
Thanks
Bob

A bad ground cable 'ground strap')between the battery and the grounding point (visible when the tool tray is removed). These can often appear whole, but have corroded under the plastic cover. Connect with a jumper cable and see if things improve.

Then, check the positive cable serving the alternator.

I'm not sure if it is the same on a 1988 928, but on my 1985 928s Euro, if you happen to leave your turn signal/flasher on (say when you have just turned into your driveway and parked your car), when you turn the ignition off, the front and rear parking lights on the side your turn signal was indicating come on. and will stay on overnight, or for however long until you return to the car., and certainly drained my battery the first time it happened!

David

First question: Do all of the interior lights work as-designed? Do they come on when a door is opened, and go off after it is closed? One of the most common battery drains is a fault in this system. Every interior light has a three-way switch - OFF, ON, and AUTO. The switch is either a small knob on the lens, or the lens swivels to one of three positions. Pay special attention to the light over the interior mirror and to the lights on the hatch.

Next question: Does the car have an aftermarket sound system? If so, it is common for the installation to be a problem.

Next question: Does the car have an aftermarket alarm or remote-start system? Very common for these installations to be a problem.

I have heard of this signal light condition before and for some reason i think it is normal on some models but I'm not sure.
On my car when I shut it off, the dash will stay lit until I cycle the key in the door lock, then the car shuts off what I assume is auxiliary power.
Thats all I know.
I believe the discussion was on rennlist if you want to search there.

The turn signal situation is for European parking on tight city streets, where you are required to actually have "parking lights". As far as I know, all 928s have the feature, where you can leave the parking lights burning on one side. Runs the battery down less than leaving both sides on...