Hi All,
1984 300D turbo California car Burgundey ( should be banned from the board just for that), according the previous posts checked the pickup/sensor at the rear of the engine all OFF gives me 1.9k ohms, engine running about 900 I guess, getting 4 volts ac these both are ok, so the next thing I followed was the side kick panel passengers side, see attached pictures, the little plug towards the bottom marked EGR this thing will pull out as is captive but it can be turned/rotated and pushed back in I think six positions, ofcourse I did not not the original position anyone have the idea what it might be or how to determine what it should be, and is the black box the EGR controller?? Help
Fareed

Try 'em all till it looks right.

The problem with your tach is probably the relay on the passenger side behind the glove box to the far right. It has a fuse that could be bad, or the whole relay could need to be replaced (that is what mine needed).

If you look closely at your own picture of the plug end, you will see a plastic protruding notch followed by a round plastic dot that have to be lined up properly to fit back in. It looks to me like it only fits back in one way unless it is forced.:D