Ground is the black wire on pin E of the switch. What they guy told you is possible. Consider that the switch may be bad and pulling more power than it should. If that happens the fuse should blow. If the fuse is too high of a rating..it may allow too much through.
All the power and module are under the seat. I don't believe they have anything to do with the power to the switch. Power to the switch is low power. The only purpose of power and ground to the switch are for it to tell the module to turn on. Something at the switch is drawing more power than it should or ...wires are pinched/restricted.
