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Old 06-01-2013, 06:22 PM
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Exclamation 300sd challenge

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.


Last edited by beccajo; 06-01-2013 at 06:47 PM. Reason: more detail
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Old 06-01-2013, 06:37 PM
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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)
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Old 06-01-2013, 06:49 PM
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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
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Old 06-01-2013, 08:34 PM
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This type of problem is so common on most makes of cars. I am really surprised your two mechanics could not run it down.
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Old 06-01-2013, 09:18 PM
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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.
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.
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Old 06-01-2013, 10:16 PM
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Originally Posted by kerry View Post
Have you tried jumping terminals 1 and 3 in the junction box (next to the alternator [on the passenger side frame rail] if it's a 126)
^ 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)
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Old 06-01-2013, 10:28 PM
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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.
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Old 06-02-2013, 03:08 AM
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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.

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Old 06-02-2013, 11:12 AM
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Originally Posted by Skippy View Post
Check for voltage at starter solenoid with key in start position.


You need two people.
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Old 06-02-2013, 11:29 AM
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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.

Last edited by barry12345; 06-02-2013 at 11:42 AM.
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