1991, 300CE with electrical problems: MAT (Omega) alarm system - old, after market installation.

Can anyone tell me what relay / fuse or other device can affect remote/ keyless entry and possibly (send voltage to radio when key is turned off.)

Which relay and where is it hidden, if that is the cure?

All the fuses located under the hood are OK. But, I can not tell what (after market?) hidden relay may be tied to the radio and affecting both of these symptoms.

Symptoms: Radio stays (on) with iginition key off, and remote (keyless) door lock works sporatically, only to lock the doors.

The Mercedes shop manual on 2 CDs is of such poor quality and limited scope that following that wiring chart offers too little information.

And, the MAT - Omega owners' manuel offer limited insight.

Thanks in advance for any help!

jsbick, keyless entry is not standard on a 1991 300CE. Who installed it and when? That seems to be the cause of your problems. The radio can be played without the key in the ignition by simply pushing the power button, but should turn off after 1 hour.

__________________
Fred Hoelzle

Thanks for your advice.

However, the radio should be off when the ignition key is off. And, the keyless system became faulty at the same time as when the radio began staying on even though the ignition key is off and removed.

Seems like a fulty relay. Probably alarm system relay but I have no helpful wiring diagram to find and test the relay.

Hope to hear from someone, whom has experienced this problem and found the solution.