2001 Ford Windstar Mirror turn signal

Best guess would be a short to ground in the wires to the mirror lamp. I would start with checking the wires from the mirror to the body harness, sounds like the insulation from one of the wires is worn though and shorting to the body or another wire.

The usual suspect is in the conduit between the door and the body of the vehicle. Check there first, if that isn't it, check where the wires exit the mirror into the door.

Just a few ideas, hope they help. Let me know.

Dan