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Starter help - 77 R107 450 SL

506 Views 4 Replies 5 Participants Last post by  RaceDiagnostics
I am befuddled with my starter issue. I have a new starter that I bench tested with existing my battery. It worked fine which is expected with a new starter/solinoid. I attached the car's wires to the new starter but did not fasten to the engine/flywheel. Tested with a voltage tester, I have power to the starter and solinoid when the key is turned. Power to solinoid is off when key is turned off. I go to turn the ignition on and nothing. I first thought since the starter is not touching the engine, it wouldn't have a ground. So I connected a ground jumper from the engine frame ground to the starter. Still nothing. Relay is turning on (clicking) when I turn the key. I even replaced the ignition switch as I thought that no could have been the issue. Unscrewed that and turned the ignition switch with a flat head screwdriver and still nothing. I even used a jumper wire from battery positive wire to starter positive post and it turns on so I know the starter works but not with the car wiring. But that is completely bypassing the solinoid. Any help would be greatly appreciated.

Update : I switched the relay with another relay with the same rating. Same problem.
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Your description of key turned on and key turned off is too vague. Lets call ON where the key is in the engine running position. Call START where the key is turned all the way to the right and you are trying run the starter to crank the engine.

According to this wire diagram you should have 3 wires connected to the starter and the starter will need to be grounded. 1 wire is connected to the battery at all times, labeled circuit 30 in the diagram below and is the large stud coming out of the starter solenoid. The other two are the two smaller studs coming out of the solenoid. They go to the starter solenoid and ignition sytem as follows.

With the ignition on there should be no current coming out of the starter solenoid at pin 87 in the diagram. Pin 87 should go to a fairly large violet wire and will go to one of the smaller terminals at the starter. That terminal is labeled 50 in the diagram below and may be labeled 50 on the starter as well, or it could be labeled "S" or possibly something else in the German language meaning start, or it may not be labeled at all.

A smaller, looks like a red and violet wire on the starter goes to the ignition system to by pass one of the ignition system ballast resisters during start up. In the diagram below it looks like that one is labeled 16 on the bottom of the starter and may be labeled 16 on the starter or "I" or in German accordingly.

Check that you have 12V at the large stud on the starter at all times.
Check that you have 12V on the other two terminals with the key in the start position.
Check that the 2 smaller terminals are on the correct post.

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