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  #1  
Old 10-29-2017, 12:44 PM
BenzEnthusiast's Avatar
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Location: Manteca, CA
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560SEL Won't Turn Off... Sometimes

My 560SEL recently started having this issue where it will stay running after removing the key. I figured that it was just a worn ignition switch and replaced the whole assembly with a new one from the dealer. Yet, the car will still stay running sometimes. Now, when I turn the key to the off position it will stutter and then rev up like it would if you were to restart it. Almost as if I am inturrepting the power to the engine for a moment and then it continues to run. Everything in the car acts normal otherwise and it only happens sometimes and it is a difficult problem to recreate.

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1992 300D 2.5 TURBO

1991 560SEL M119.960

1991 420SEL Parting out.

1986 500SEL ECE Going to be sold soon.

1986 300SDL TURBO Going to be resurrected... eventually.

1992 190E 2.3 Sold to my brother.

1985 190D 2.2 Sold to a close friend.
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  #2  
Old 10-29-2017, 12:47 PM
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Join Date: Dec 2011
Location: Manteca, CA
Posts: 207
By the way, when this occurs I unplug the fuel pump relay to turn it off and I unhook the negative battery terminal. Also, I check the diodes in the alternator and they test fine. Any help would be appreciated.
__________________
1992 300D 2.5 TURBO

1991 560SEL M119.960

1991 420SEL Parting out.

1986 500SEL ECE Going to be sold soon.

1986 300SDL TURBO Going to be resurrected... eventually.

1992 190E 2.3 Sold to my brother.

1985 190D 2.2 Sold to a close friend.
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  #3  
Old 10-29-2017, 01:16 PM
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Join Date: Feb 2011
Location: Modesto CA
Posts: 2,961
BE:

Try unplugging just the D terminal from the alternator when the symptom next occurs.
The field exciter circuit has its own set of three diodes, separate from the six diodes in the main power circuit.
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  #4  
Old 10-29-2017, 01:44 PM
BenzEnthusiast's Avatar
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Join Date: Dec 2011
Location: Manteca, CA
Posts: 207
Forgive my ignorance, but which one is the D terminal? Is it the smaller of the two wires that are attched to the studs on back of the alternator?
__________________
1992 300D 2.5 TURBO

1991 560SEL M119.960

1991 420SEL Parting out.

1986 500SEL ECE Going to be sold soon.

1986 300SDL TURBO Going to be resurrected... eventually.

1992 190E 2.3 Sold to my brother.

1985 190D 2.2 Sold to a close friend.
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  #5  
Old 10-29-2017, 01:50 PM
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Join Date: Dec 2011
Location: Manteca, CA
Posts: 207
It's acting almost as if circuit 15 and circuit 30 are shorting, but I can't find any damaged wiring. Is it possible that the factory alarm module could be shorting them? It does connect to both circuit 15 and 30 and it is intermittent. Maybe I'll unplug my alarm module.
__________________
1992 300D 2.5 TURBO

1991 560SEL M119.960

1991 420SEL Parting out.

1986 500SEL ECE Going to be sold soon.

1986 300SDL TURBO Going to be resurrected... eventually.

1992 190E 2.3 Sold to my brother.

1985 190D 2.2 Sold to a close friend.
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  #6  
Old 12-12-2017, 02:12 AM
BenzEnthusiast's Avatar
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Join Date: Dec 2011
Location: Manteca, CA
Posts: 207
I haven't had the problem ever since I disconnected the wires from the back of the alternator to check them. Perhaps they didn't have a clean connection until I reattached them this last time.

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