When I was troubleshooting my '86 BMW 635, I connected the ammeter (actually a multimeter set to the OHMs setting (Looks like a greek Omega) between the negative battery terminal and the negative battery post.

Are you saying that when you do this you show no current draw - even when you open a door or turn on the radio?

Are you sure that you have the proper range set for the meter? My electronic multimeter automatically adjusts the range (from 10s of Ohms to thousandths of Ohms), but if yours is an analog device - it may need to be manually set to the thousandths or hundredths of Ohms range in order for you to see any current draw.

Let us know if this helps - this troubleshooting shouldn't be this hard. Hopefully your meter is working.

Regards,
Troy
1995 E420