mercedes radio immobilizer

I have this 1992 Mercedes 400E which has a system which disengages ("immobilizer") the starter motor on the car if the radio is removed, so I'm wondering what to do if you replace the original radio with an aftermarket radio. How do you make sure the immobilizer isn't activated when you take out the old radio?Richard

I've installed many stereos in Mercedes in my day, but don't recall ever having an issue like this when replacing the factory unit. If you still have the factory unit installed, use a meter to measure each wire other than the speakers wires ( https://www.the12volt.com/installbay/stereodetail/1421.html)  while the key is in the ignition and start positions and post what you find. Measure for voltage first, then resistance to ground if no voltage is present. the12volt • Support the12volt.com

The only thing I recall was a wire that was on a tab terminal connected to the rear bottom back of the radio(does that make sense). If the alarm was armed and the radio removed, wiring disconnected, it would set the alarm off. I believe the wire was brown with a blue stripe. Hope this helps.

That rings a bell... since it was connected/grounded to the bracket, just connect it to ground now.  the12volt • Support the12volt.com

You could also connect it to the back of the new radio to function as it was intended. the12volt • Support the12volt.com

Thank you all. Yes it's difficult because the factory radio had been replaced years ago with a super sonic system which the former owner took with him and left me without guidance of which wires are for what purpose. Plus you'll recall there's an OEM fader control and so that means more wires in the console, and with the help of a good Samaritan from this forum, had help in uninstalling a Vipre for which the prior owner didn't give me the remote, and/or was malfunctioning, and/or the OEM immobilizer is malfunctioning. So as I'm trying to get a new radio installed, simultaneously for no apparent reason the anti-theft system will decide to engage and I can't start the car. At the worst possible times, as when I'm in a no standing zone, or a hundred miles from home. Dozens and dozens and dozens of posts on the Mercedes boards regarding this issue. It's hell. The whole situation has just been bad luck for me. I bought a really nice Pioneer DEH-X9500BHS which not only can't I install until I figure out why the OEM immobilizer kicks on, which now may be due to that ground wire and intermittent connection, but as well when I put a power lead from the car to the yellow wire on the radio harness, and then connect the ground to the radio (just to test the radio goes on), I get a short circuit and it seems the car's electronic control module is going to short out. The car keeps running, but all lights and electronics go dead for three heart-stopping seconds. I'm not a complete idiot and know power from ground; I just don't know what is going on. Then I took the radio back into the house and connected it to a power supply (small portable auto jump start unit); power and negative to yellow and black, and the radio won't power on. I just don't understand it. The fuse is not blown, and the radio is brand new out of the box; not a refurbished or something. Can't possibly be bad. Just so frustrating. Sorry for venting; thanks again. Rick Bryan New York, NY Richard