I agree w/ PawoSD....I just did this job in the wagon last week due to bad teeth non my regulator gear. I had a used replacement for my regulator that came with the motor. I wanted to use my original switch and wiring, so I just unsoldered the wires from the original one and resoldered them onto the replacement. Was able to leave the wiring in place in the door.

So in your case, just cut the wires at the old motor and solder them to the motor terminals on the replacement.

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Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT