The test the brother was doing was with the car off, doors closed. Put a voltmeter in place of the fuse - if you have a battery voltage reading, you know the circuit has power and a ground. Some circuits are supposed to, some not. He probably pulled the fuses/wires on those circuits not supposed to be drawing voltage. He's on the right path. Get a schematic and keep going - you'll find the gremlin.

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Thank You!
Fred
2009 ML350
2004 SL600
2004 SL500
1996 SL600
2002 SLK32
2005 CLK320 cabrio
2003 ML350
1997 C280 Sport