78 300SD (W116), right rear window regulator goes down, won't go up (motor doesn't even click).

Have the regulator out and motor removed, about ready to go back at it and see if I can re-assemble in the up position and leave the switch out just to make sure it doesn't get run down by playful hands again .

Any ideas why I can get the motor to run fine down, but not up? Can see that there are only two wires (neither appear to be ground?) going into the motor; tried using the switch from the passenger side door, same results.

Side note, that may well be a red herring: center console switches for the passenger side are basically hollow (on my list parts to replace).

__________________
1961 220b: first project car - sold.
2000 CLK 430: first modern Benz - sold.
2001 CLK 55: OMG the torque!!! - sold
1972 280SE 4.5: Baby Gustav
1991 300TE 4Matic: Gretel the Snow Bunny - sold
1978 300SD: Katz the Free Man - given away
1980 Redhead: Darling Wife