450SL power Antenna switch wiring
 

Hello everyone,

I am new here and have a 1976 450 sl where the antenna does not work. I pulled off the cover for the motor and found the wires had been disconnected. The previous owner put in an aftermarket stereo so that see could listen to audio books. However, the radio does not get very good reception since the antenna does not work.
So I measured the voltage of the wires going to the motor and found that I get 12 volts. When connecting the wires to the motor , the mast goes up, but will not come down. If I reverse the wires, the mast goes down. This tells me that the switch on the dash must reverse the polarity to operate the antenna motor.
Is this correct?
If this is true, could I have a bad switch, or does this after market stereo not have the proper circuitry to operated the antenna properly. I still have to original radio if this fixes the problem.
Any advice will be appreciated.

Tim