You should have a constant 12V to the motor, a ground, and 12V that comes from the radio. If you have those signals, then the motor may be fried, or the "tail" that winds and unwinds to lower and raise the may have jammed it. You can take the case apart and check it out. If the tail is bad you will need a new mast. If the motor is toast, Palo Alto Speeometer can rebuild it.
If you want to go manual, then just cut the tail off.
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe