Can early electric window motors be replaced with newer motors?

I would like to replace the window regulators and electric motors in my 1972 911S with regulators and motors from a 1974-1976 model. The newer regulators are a bolt-in replacement for the old regulators. However, the newer motor has two wires (green and black) compared with three wires on my original motor (green, black, and brown). The three wires from the original motor connect to a wire harness in the door. The window switches also have three wires (all red with black, white, and no stripes) coming from the same wire harness in the door.

My questions are: can I replace the early motors with the newer motors? Is there a problem if there is no brown ground wire connected to the harness from the newer motor? Will the original switch still work if I leave the three wires connected to it or do I have to change something? Is there anything else I need to do to replace the original motors with the newer motors?

Thank for helping!

Guy

Yes, you can. I'm not sure if my switches are the same as yours, but with mine I added a ground from the junction block in the door to the fourth terminal on the switch and everything worked. Check the post below for the way I wired my '72 after using the later motor.

http://forums.pelicanparts.com/porsc...er-switch.html

Here's the relevant diagram

Thank you Mike, your suggestion works! My window switch has five prongs instead of the four in your drawing, with three wires connected to the wiring harness. I connected a wire from the ground in the harness to one of the empty (top) prongs on my driver's side switch and the '74-76 replacement motor works!

Guy

Cool! Glad it worked for you.