1988 560sl. shut the key and took it out but the engine runs normally. will not shut off. disconnected the battery but still running. turned the key ..take it out no help. had to flood the engine to shut it off. any help please

Try this:
Remove the small wire from the alternator (usually blue). Start engine, then turn key off.
If it shuts off normally there are shorted diodes in the alternator. If it does not shut off, look to the key switch.

Rather than flooding the engine to stop, pull the crank pickup wire (green coax) from the ignition box (EZL).

where would the ignition box be located on a 88 560sl

also the dummy lights on the dash will not shut off unless I disconnect the battery and reconnect

found the ignition box..cant see any single wires to the alternator. it looks like one plug. very hard to see anything behind the alternator. no space

cj:

There is a device called the Over Voltage Protection (OVP) relay that is responsible for a number of strange symptoms when it fails, although keeping the engine from shutting off is a new one. It often has a red top, with a clear lid over it, and one or two 10A fuses under the lid. Check the fuses, and replace if melted.

The lights remaining on is a clue that power is being fed back, either through a defective relay, or through defective diodes.

would you rule out the ignition switch?

The switch cannot be absolutely ruled out, however it's unlikely that the indicator lights would remain extinguished when you reconnect the battery if the switch were the culprit.

you hit it on the head. disconnected the plug to the alternator and all worked as it should. the strange thing is the alternator is 4 months old. thanks for your help. will change out the alternator.

ok got another alternator and all was good. worked great. now 2 days later same problem. engine does not shut off.. any help..please

this is getting stranger.. I unplugged the alternator and plugged it back in and all is normal again. might the be a relay that gets stuck? my thinking. anybody??

cj:

See post #6 from 12/24/14. Have you located the OVP yet? It is behind the right kick panel.

fr
located the OVP. there was corrosion all over the fuse. replaced the fuse and cleaned it all up. hope this solves the problem for the long run. Thanks again for your help.

If the OVP was showing external corrosion, it should be replaced.

This device controls power routing to critical items, ECM, fuel pump, crank position signal, etc.

Check the part number on yours, to verify it has not been superseded due to various issues.

I have attached the OVP list for your car.

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