Instructions for Connecting Garage Door Opener to the
Wiper Stalk Phone Switch
E36, E34, probably older 7's, 8's and E38's have a BMW cell phone operable using the in-dash display and the turn-signal and wiper push-in buttons. Since most of us won't buy the BMW phone, a garage door opener connected to it is useful to some.
The wiper stalk supplies a ground through a black/green/yellow wire which terminates under the rear console (for the phone) in my E34. Also there is a violet wire to supply +12V for the opener (so you don't have to ever replace batteries).
In more detail, if you're also an E34'er of the same year as mine (probably works for the others) - you should find 2 small yellow plugs, one has three wires and the other two. The three wire one is yellow/red, black/green/yellow (the one you want), and yellow/red/white I believe. The two yellow wires will be jumpered together with a plug - the yellow/red goes to the turn signal push-in so the jumper lets the OBC be thusly activated in the absence of the cell phone.
The wires on the other plug are brown and violet with no attachments.
Pop the rear plastic cover from the bottom up and shine a flashlight in. Good Luck - I'd try not removing the rear console first. (I simply cut the two wires I was interested in leaving, of course, room to resolder in the event I want to buy the BMW phone - it would be sweet). In case you're no radio expert, keep the opener antenna away from metal, the brassy bracket securing the rear of the console for example.
You have to figure out a little about how your opener works. One way is for the (+) from the opener battery to go to the opener button - another is for the + to go to the circuit and then to the switch and from the other switch terminal to the battery. Assuming the former, connect the + (violet wire) to the appropriate switch terminal and the black/green/yellow to the (-) battery terminal.-