[Spikesoftail]

Sounds like if the switch is getting hot you either:

1. have a switch that wont handle enough amperage
2. Fans that are going bad and pulling too much amperage

Fans pulling too much amperage would be my though, something tells me that the thermostat that controls the fan is burned out, being as though you've got it jumpered to a switch. That plug the major drop in voltage when its running. I'd say do and amperge draw test on the fans, or find some good used ones and plug them in.