Auxillary Cooling Fan - '86 300D

Can anyone diagnose problem from the following info:

1. Aux fan does not spin when A/C is on.
2. With car running, measured 9.01 volts at closest plug (has two wires) to the fan. Had to jump the high pressure switch to get 9.01 volts. (This seems to indicate that the high pressure switch is bad?). With measured 9.01 volts - the fan does not spin.
3. Checked ground wire a same plug and have good ground.
4. With battery voltage jumped to fan side of plug, the faqn spins fast.
Question: Should the fan spin when 9.01 volts avail?
5. Measured ~10M ohms across pre-resistor. Is this appropriate?
6. Can anyone verify that either the fan or the preresistor is good or bad?

Thanks in advance
Rick