Sorry if this has been posted in the past, but I searched and couldn't find the info, so I did a little sleuthing with the multimeter.

This is from my 85 300TD, others are probably different...

Klima Pin 15, Socket Pin 5 - +12V when key is on
Klima Pin 31, Socket Pin 1 - Ground
Klima Pin 87, Socket Pin 7 - to compressor clutch, supply 12v here to engage compressor
Klima Pin KL, Socket Pin 10, +12V here from CC unit signals AC to switch on - this signal passes through the low pressure cutout on the recv/dryer, the high temp cutout at the same place, and the freeze cutout on the evaporator.

So, connect 15 to 87 to engage the clutch, +12V between KL and 31 is the signal.