I had a similar problem with my 2005 ML270. It turned out to be a faulty All Activity Module and cost about $Australian 1500.00 to replace BUT there are many threads on how to check for associated problems before actually replacing the unit. One such is:- http://www.benzworld.org/forums/w163-m-class/1591416-ml270-cdi-high-beam-constantly-3.html
But you will find 43sqd really understands this area if you answers his questions andfollow his advice.
But you will find 43sqd really understands this area if you answers his questions andfollow his advice.