Well I'll bump you again. I looked in the past and I looked again. The diode is shown to be non existant as of 1989.

I have looked in three different places and all three are slightly different in the area that would explain the key on operation. The way I read the diagram after 1990 there is no power with the door closed. The wire from 15R that should power the relay says it doesn't exist after 1990.

Since the doors are obviously powered with the key on all the cars I have seen. I presume the power must come from 15R. But the alarm system or the locking system might be in the way. I looked but I don't see the connection.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician