Just fixed a customer's 89 Multivan with power mirrors.  Problem was both
mirrors were inop.  Popped the door panel on the driver's side expecting to
have to do a long and involved troubleshooting session with my multimeter.
The plug that goes to the mirror switch had come unplugged!  Plugged it back
in, everything worked great.  No fuses popped or anything so I assume that it
was not intentionally unplugged in the past.  Apparantley the plug was either
not plugged in properly to start with and wiggled loose, or maybe the guy
forgot to plug it in when he put new speakers in the doors.
Something for folks with non-working mirrors to check.
I plugged it back in and used aluminum tape (found at Home Depot) to be sure
that it couldn't come loose again.
Now to write the bill for 3 hours of labor :)

Hope this helps,
Ken Wilford
http://www.vanagain.com
John 3:16
Phone: (856)-765-1583
Shop:   (856)-327-0027
Fax:     (856)-327-2242