Bong,
You might be interested in this. The fan relay on a mini van I have went out, so I wired the fan directly to the ignition switch. It worked great and gave enough time to get an after market fan ($75 vs. $350 for an oe unit from the dealer). The problem was that when I turned off the engine it Dieseled for a few seconds. I never connected the two until I mentioned the 2 problems to a mechanic. He said that when you turn off the engine the fan winds down. Since the fan motor is DC, as it winds down it goes from being a motor to being a generator. The voltage it produces as a generator back feeds into the ignition system and causes it run on a bit. This is not much of a problem, but he said that the voltage backfeed will damage some of the car's computer circuits. I don't know if this is possible w/ your MB but you might ask your mechanic.