Originally Posted by Diesel911

On the W123s the Motor is not grounded through the Chassis like a Starter Motor is.

The Window Motor Direction Change is done by the Window Switch alternating polarity; the Ground is though the Window Switch.

That means if you are probing with a Volt Meter and one Probe of the Volt Meter is grounded to the Chassis no matter which direction you move the Window Switch you will get 12 Volts.

If you were to hook your Voltmeter in series with one of the Window Motor Wires when you push the switch one way you would get + 12 Volts (on a Digital Volt Meter) and when you push the other side of the Switch you would get a -12 Volts.