Thought I would post my fix for this issue. The rear lamps on my 06 E320 are in fact LED lamps and the voltage supplied to illuminate the rear running lamps is not enough to switch the relay input on the EU/US lamp converter/isolator that I am using. I tied the running lamp input on the converter to the licence plate lamp and that works. I had removed the licence plate bulb while looking at the circuit with a VOM. I did not know that the two licence plate lamps are controlled separately and that the car computer turns off a lamp when it sees an open circuit as would be caused by a burned out bulb. These two things caused me to go round in circles until I figured out what the computer was up to.

I have a 06 E320 CDI and plan to tow a light trailer with it. I have a hitch hooked up and am attempting to hook up the lamp circuit. I am using a EU to US converter box which also isolates the circuits. The first thing I found was that the car rear parking lamps are low voltage LEDs and the circuit does not provide a high enough voltage to pull in the converter box input relay, looks like about five volts using a VOM. So, I have tried to use the licence plate lamp circuit. This is a 12V incandesent lamp rated at 5 W. Well this circuit does pull in the converter box relay but shuts down the circuit after about 3 seconds. The two licence plate lamps are powered and monitored separately, (??). The one lamp that I have tied into is turned off by the car computer and the other remains on.

I have thought of removing the right licence plate lamp which is where I am tied into to reduce the circuit load. And I have thought of buying a very low power relay to use to reduce the new load I am presenting to the circuit. But I wonder how MB does this hook up in Europe. They offer a tow pkg in EU and have the trailer lamp wiring tie in installed. Does anyone know were I can get a running lamp signal to use that will not fault the car computer?

thanks,

Mark