1986 735i factory cruise control

I am having no joy with locating a wiring diagram for the car, if anyone can help I would be very grateful. (The cruise will not engage at all.)
Any ideas would also be appreciated.
hank you

Check here:

http://www.stormpages.com/countchocula1/bmw/etm141.htm

Forgot to mention that the cruise control "brain" is located behind the speaker in the driver's side footwell. Sometime the can get water in them. One fix ma be to pull the unit out and see if it is wet. Possibly drying it off could be the fix. If not, used cruise control 'brains" are usually available on ebay.