My 1980 300 d 123 drains battery in 2,3, or 4 days. I have isolated to a 10 pin connector located under dash, passenger side against floorboard. Only two of the ten connectors are hot at all times. The problem is there., cause when I disconnect battery does not discharge. I find nothing that is disabled when the 10 pin is seperated and car runs fine. However auxiliary pump for heater does not work, license lights intermittent etc. What do those two " hot at all times" energize?

i would try disconnecting the A/C servo and see if the drain goes away, on that model, the servo is the first likely suspect for a drain

Carson, thanx for the reply. I have awhole new direction and awareness of the cars system as a result!!