300SD won't start or crank
 

Last night my car decided not to start. When the previous starter was on the way out it gave warning by having a split second delay before cranking the engine, the current starter's failure was out of the blue.

This morning I installed a used starter that Sixto gave me which we tested before he gave it to me. I have the same response now as I did last night, just a little ping sound coming from the center console, but nothing else. The battery and alternator are good. The car is in Park. I'm guessing neutral safety switch at this point. I have a spare used one in my garage. How can I test or bypass the NSS that is currently on the car? Thanks

I just checked to see if I get reverse lights with the key in running position, and I don't. Bad NSS, right?

I just got the engine to crank by bypassing the ignition system. I'm going to swap out that NSS and hope for the best.

I am sort of going through this with the 84 300D. Except mine will start in neutral.

In my case the shifter does feels kind of odd. Could be I need shifter bushings, but I have not taken time to look into it.

Note on a W123 there is not much space between the area where the Neutral Safety Switch is and the tunnel the transmission is in. I have not got into it yet but it looks like at the very least the tail end of the trans needs to be lowered which means lots of stuff needs to be removed to do that.

There's a junction box on the fender liner just to the side of the alternator on 126's (I think). You can jump two terminals in that box to start if you need to. It could be a bad NSS or a bad ignition switch or poor connections somewhere in the circuit if jumping those terminals causes the starter to engage.

The NSS was the problem. The car starts up fine with the spare NSS I picked up from PnP several years ago.

I'm not frustrated over replacing the starter since the old one would occasionally drag on the fly wheel.

I'll be keeping a jumper wire in the trunk with my other emergency parts in case this happens again.

Was it tricky to get it adjusted so that your backup lights turn on in reverse? My new nss needs a tad of adjustment.

Another thing that can cause this is shifter bushings. There are 4. Three of which are easy and can be changed from above. There is a vid on youtube posted by the guy that shall remain nameless where he made a fancy schmancy tool to install the bottom bushing. I didn't need to do the bottom bushing to get enough play taken out so that everything works.

I could move the shifter through its range while holding the key to the start position and it would crank & start. This may be a way to distinguish between shifter bushings and a bad NSS. A bad NSS will not crank. An out-of-adjustment switch may crank.

The easiest way to diagnose NSS issues is to run the shifter through the gears and stop in N or P. If the engine cranks after doing that, it's likely shifter bushings, not the NSS itself. My SDL would not start when parked on any sort of incline with bad shifter bushings. Would have to run the shifter down and back into P to get it to crank. Since replacing the bushings, never once have I had an issue again.

Other clues are a rattle from the transmission tunnel or a click/clink when changing gears with a "sloppy" feeling shift lever. With new bushings, the shifter is very "tight" feeling.

My reverse lights are working, but not because I was conscious of any adjustment. I just lined up the arm of the switch to lock into the transmission lever. I'd guess that you have some play in the lever due to worn bushings or some other worn out part.

The bolts that hold the NSS to the transmission go through slots in the NSS so there's something like 5* of adjustment between the NSS case and the plastic lever that engages the metal transmission lever.

Sixto
83 300SD
98 E320 wagon

Bolts? ha ha. Mine had one. Maybe my switch was just out of adjustment and not bad. The one bolt was on there pretty tight though, there wasn't any play.

You can bench test it with a continuity meter. It should be easy to test pairs that make contact as you move the lever.

Sixto
83 300SD
98 E320 wagon