Can't figure out Trans switch '91 200

[Wolff <quattro200@earthlink.net>]

At least one other lister has a '91 200 tq that is leaking in a similar
manner from the mystery switch on the rear of the transmision. I have
looked at ETKA, Bentley and the fische. I looked at every wiring track
in the book, and didn't see it. I can't find the thing listed anywhere.
It looks like an oil pressure sender with two wires on it. It is facing
diagonally toward the right rear and is a few inches ahead of the prop
shaft just above the right exhuast. It was suggested that that is the
location for the 5th gear switch for the upshift indicator on earlier
cars. Am I supposed to have an upshift indicator? I would like to find
out what it is so that I can order a new one without having to fight the
old one out ahead of time.
Thanks,
Wolff