Well, It had been a long time since I have been this stumped. Here are the basics;
1981 300SD, All of the sudden, and overnight, will not crank with the key. The car will start by jumping the battery positive and the solenoid lead at the terminal, and the car runs normal.

I first began by checking and cleaning the ground strap from the battery to the chassis, and the chassis to the starter. I also have eliminated; starter (known good, and just tested), ignition switch, (known good, just replaced), and I just replaced the neutral safety switch. I had really counted on this being the culprit, as the back-up lights do not turn on when in reverse.

My thoughts are that there may be a harness connection between the neutral safety switch lead and the main harness that has come loose, Other than that I do not have a clue.

Thoughts?

Robert

How are the selector bushings? If they are worn out, it can cause the same symptoms.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

The selector bushings are tight, and in good condition. Until this happened last week, I have not had any notice of trouble, such as having to jiggle or adjst the gear selector to get the car to start.

aftermarket alarm?

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1967 250 S
1967 280SE
1968 250S
1971 280 SE
1973 220
1974 280 S
1975 450 SEL
1976 220 D
1979 300SD
1983 300 SD
1985 230 TE euro
1986 280SL
1986 500 SEL euro
1986 190E 2.3
1990 300 SE
2003 C230 K
2004 C230 K
1987 560SEL
1987 300SDL now in canada
2005 C230
1998 C43 AMG Sold to DON
1993 190E 2.6
300TD Former daily driver Totaled
current:
R320 CDI
Ram 2500 Cummins

No alarm...

But good question though.

Problem Solved:

After checking the harness below the car, I started above and inside. It seems that there is a six pin connector on the drivers side of the transmission hump, adjacent to the accelerator pedal. Once I removed the console side panels, I could see that the connector was slightly apart. Once I pushed it in completely, problem solved. Once again, these are simple cars, and with tenacity despite a defeated feeling, most issues can be solved.

Thanks for those who gave this issue consideration and thought!