Ml 320 GPS Problem

[Shermanus]

Here is my problem, which seems to have developed in the last 3 months:
2001 Mercedes ML 320. Had a Mio, worked fine until 3 months ago. Thought it may have died, got a TomTom 630. Worked out of the box-for 1 day. Cannot find GPS. Replaced it with a 730- same story. TomTom had me reinstall the software. Same result. Here is the odd thing: Parked, with no connection to the car, has full reception. Turn on the ignition (not engine) GPS gone ! Went to Mercedes, they are puzzled but tell me that a search for interference would result in about a 1000 bucks in labor. Tried a TomTom 910> same story after 1 day of working fine. What now ? I pulled Fuse F10 and the problem goes away, but the SRS light comes on. If I then switch on the radio: GPS gone again. So it is obviously the car, not the Gps. What does fuse 10 do that kills the Gps signal?