When I installed driving lights on my 05 MCS cabrio (xenon lights) a couple of years ago I wanted them to be controlled with the high beam stalk. However, after testing all the wires in the harness I couldn't find the one that controlled the high beam and settled for just using the driving light switch. After reading some of the threads in this forum I figured that I had done something wrong. So I just went out and tested them all again. Every wire going to the harness (except the heavy brown ground wire) is hot with the low beams on (high beams off). I'm sure the high beam wire is the heavy yellow/green wire on the far left (looking from the front) but it is hot with only the low beams on. I don't have the foggiest idea what is going on and could use some help. Thanks.

 

Maybe there is a relay in the BCM (or somewhere) that awaits a ground (but always has power sitting there and waiting) when the stalk is pulled to the high beam actuation point.

 

I am pretty sure it has something to do with the way the car controls the lights, it doesnt use actual relays, just modulates current (i think). Going from the drivers side I am pretty sure it is the yellow wire with the green stripe for the high beams.

If i remember correctly the way I found this out was by comparing the voltage under load with the lights on. Basically I scraped a little insulation off the high beam wire and compared the volatge that my meter gave me connected to the that wire to the voltage of one of the terminals inside the light housing. At least that is what I think I did...

 

I'm sure it is the yellow with a green stripe, also. But it is still hot with just the low beams on. That is where I have my driving lights connected and they operate with the low beams (with or without the high beams). Where did everyone else connect the wire to operate the driving lights with just the high beam? Thanks.

 

Yellow/green sounds right - I hooked mine up at the BCM (located on the outside of the passenger footwell) per the OEM instructions. Note that at that location, it's a small wire, not a 'heavy' wire.