The car isn't cranking at all but lights and radio come on. That's why I think it would be electrical in nature.

My battery is new, within the last six months. It holds it's power just fine, there's no drain except for a tiny bit from the radio. The alternator is new. The power cable to the battery is new too, and the ground has been cleaned. The starter is new. There was no sharp clunk the last time in ran. The ignition switch is also new. And of course the shifter is in park. Power is being sent to and from the neutral safety switch. I've wiggled the shifter while turning the key and nothing happened. The back up lights work. The tumbler doesn't seem sticky, the key comes out just fine. The glow plug light comes on, all the glow plugs have been replaced in the past year. All the wires to the starter test 0 resistance. No fuses are blown.

Any ideas? I'm pretty experienced, and I've had two other mechanics look over the car and they're stumped too.

Thanks!

It may be ideal to cite the problem(s) you are experiencing. As in, are you trying to diagnose why the car isn't turning over? (my guess)

__________________
2010 VW Golf TDI Cheetahhh
2008 GL320 CDI 4matic x2
2006 E320 CDI
1983 200 (Euro 5spd)
1982 300TDT
1981 300D (617.951 swap)
1966 200D

Have you tried jumping terminals 1 and 3 in the junction box (next to the alternator if it's a 126) or hot wiring the starter terminal directly from the battery?

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

This type of problem is so common on most makes of cars. I am really surprised your two mechanics could not run it down.

measure voltage drop to confirm that no corrosion is keeping it from turning. There has to be a bad part or connection or the system would work.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. Probably up for sale in the fall 2020 still have it. 85TD beginning to repair to DD status. Waiting on shop to do minor but more than I can do rust.

^ thiiiiiiiisssss

__________________
1982 300sd from craigslist $800 greased on one tank with NO CONVERSION in the Hot Texas Sun. (currently dead & awaiting engine damage investigation and/or longblock swap)
new daily: '03 vw 5speed jetta tdi wagon. bagged&chipped

Does the engine turn at all when you try to turn it over by hand? Try turning it manually with a socket wrench on the power steering pump.

__________________
"I have no convictions ... I blow with the wind, and the prevailing wind happens to be from Vichy"

Current
Monika '74 450 SL
BrownHilda '79 280SL
FoxyCleopatra '99 Chevy Suburban
Scarlett 2014 Jeep Cherokee
Krystal 2004 Volvo S60
Gone
'74 Jeep CJ5
'97 Jeep ZJ Laredo
Rudolf ‘86 300SDL
Bruno '81 300SD
Fritzi '84 BMW
'92 Subaru
'96 Impala SS
'71 Buick GS conv
'67 GTO conv
'63 Corvair conv
'57 Nomad

Most likely starter be no more good. Less likely possibility is that wiring from key switch to starter is failing to energize the starter solenoid. Check for voltage at starter solenoid with key in start position.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 379,xxx miles
08 Triumph Street Triple 35,xxx miles, lowered 10mm in front, Pirelli Angel GT tires, EBC HH brake pads, otherwise stock.
88 Jaguar XJS V12 94,xxx miles. Work in progress.

^^^

This.

You need two people.

Well as Kerry mentioned your mercedes has a very good provision to divide the problem into one of two segments.. Short the contacts together in the box on the fender he describes.

If starter works the problem is in the solenoid engaging circuit. If not it is in the high current part of the sector. The high current items are the feeds from the battery and the starter itself. The solinoid portion of the circuit is basically the neutral safety switch on the transmission. Plus the electrical portion of the key switch. Plus the solenoid. I suspect you changed the key switch mechanical part but not the electrical portion of the ignition switch by the way. Plus the associated wiring and connections. If you do the mentioned test and post the results others can guide you further if needed. This is not rocket science.