My 82 240D has been a fantastic experience. Bought 18 months ago, drive daily, now has 360,000 miles--love it to pieces.
A few days ago when I tried to start it, I got no response from the ignition at all, though it had started fine continuously prior to this. I had noticed recently that my automatic transmission had developed a slight hum/buzz in the gearshift console--nothing seemingly problematic, but the gear-shift has always moved very easily between P-R-D-3-2 and, in the past couple of months, it had gradually been having a harder time finding Reverse.
Because of this change in behavior from the gear-shift and the possibly associated hum/buzz, I suspected that the ignition might not be recognizing that the car was in Park and therefore wouldn't fire when the key was turned. On three different occasions now when the car wouldn't start, I have put it in Neutral, rolled it a few feet, then put it back in Park, and the car has started. But this method has failed a few times as well, and is obviously not ideal.
Since then, I have checked connections between battery and ground, battery and starter. I have removed battery connections and cleaned them. I don't have a repair manual, my mechanical abilities could be described as "fairly low but eager to learn." I do have access to a friend's full schematics of the car.
My question is, where is the switch/mechanism that signals to the ignition that the car is in Park? Would such a switch reside in the transmission or the starter or some point in between? (Would it simply be the starter solenoid?) And is my assumption about the ignition not 'recognizing' that the car is in Park at all reasonable? Is there any way to tell whether the car "recognizes" that it's in Park for the purpose of ignition?
After that, I'd guess I'd move on to evaluate the starter and the starter solenoid, though I'm probably in over my head with those, too. I have no idea how old the starter is--it is a Bosch made in Germany.