I have seen your situation occur a couple times. I think that both events occured due to loose screws and high local resistance causing heat which melted the plastic box till the screws touched the body. At that point the harness melted. One took a bunch of the harness with it. Once the screw hits the body the blower and controls are out of the circuit. Once the fuse is repaired, the blower can be diagnosed as usual.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician