You may not have taken particular notice, but I would be very interested in knowing the Service guy's step-by-step process for solving this issue.
step one.... get out the multimeter or a test lamp
step 2............ test battery has good charge
step 3 ....... put ONE probe on the battery side terminal of the switch the OTHER probe onto the frame ground ............. confirm voltage
step 4 ....... put ONE probe on the OUT/CONVERTER side terminal of the disconnect switch the OTHER
probe onto the frame ground ................ confirm voltage
If no voltage in step 4
wiggle, rotate or kick the disconnect switch
if it still does not work it needs replacing.... Only real good brands can be repaired
most are JUNK just easier to replace it
If you are travelling ......
take the wires off the converter side of the switch .
PUT them on the battery side of the switch.
continue camping until you can get a replacement switch.
EDIT... additional
Disconnect battery before trying to work on the disconnect switch with any tools
DON"T ask!