Antenna, 1986 Audi 4000, motor pushes antenna out

Antenna works but motor will not stop—it pushes the mast all the way out.

I believe this is a matter of the stop switch inside the antenna mechanism. This switch tells the motor to stop when the antenna is extended.

Rather than "re-invent the wheel, " perhaps someone can tell lme how to set the stop switch correctly so that the antenna stops when it should.

Mileage on car—190,000
engine size—1.8 l gas