I had the same problem with my 99 ml430 and my kenwood sat/nav. I tried to find the VSS wire and could not. Kenwood told me it is a pink wire that can be found in the BAS/ESP harness, but that is like finding a needle in a haystack, and if you access the wrong one, you have big problems with traction control. So, I never hooked it up, and my nav works fine (although I get no turn by turn audio directions). I know you can buy seperate speed pulse creation gizmos (a magnet for the wheel and a sensor in the wheelwell, normally used on older cars without the pulse wire) but I never got around to spending the $200 for one and putting it in.

So, my question to you is what is this Canbus unit you are talking about? Yours (like mine) is an older ML so it should not have the fiber optic system (mine did not), nor the command system, so I am wondering what this is, how it works, and what I can do to get one, as this is the only wire I did not hook up out of a full nav/stereo/video re-wire of my truck.

FYI, MERC refused to tell me which wire it was, and told me to buy their seimens nav retrofit kit, which I did not want as I wanted a good stereo with video. All my info came from Kenwood or the shop where I bought my system.