1985 500SEL.

For whatever reason my W126 continues running with key removed and the ACC engaged/on. Push the button to turn off the ACC and it shuts down. I'm used to it so I don't care but it has resulted into some panicked calls from friends who have borrowed the car.

Any ideas? I'm sure it is back feeding somewhere through a relay but I'm stumped as to which one or ones.

It has a new ignition switch due to a different problem but it did it before and after the switch was replaced.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

I assume that your car has an Over Voltage Protection relay. If it does, i would start by replacing it with a new one. If that does not fix the problem, try disconnecting the small wire that feeds the alternator light. The last time i faced this problem the diode bridge in the alternator had burned over and did not stop charging when the ignition switch was turned off, it was bleeding +12 volts through the small wire. If you need more info feel free to PM me.

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600SEL '91
300E 4Matic '88
240D '83
280SE '77
350SE '73
The most complex systems can fail in the simplest way.
Contra verbosus noli contendere verbis, sermo datur cunctis, animi sapientia paucis.

i don't believe in the lord! He's never bought me a Mercedes Benz.

Makes sense. I'll give those two items a try.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Oops! I did it to myself. A previous owner had hacked into the over heat/condenser fan wiring harness and I straightened out the mess (I thought). I think I used a regular ground instead of using the A/C pressure switch.

Found out by unplugging the relay I had re-wired. Back to the soldering iron!

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now