Originally Posted by
mranlet
Use a relay.
Fan ground to chasssis
Fan power supplied through relay from battery
Relay switched via keyed power or fan trigger
If you're still frying stuff then there is a problem with the fans themselves.
Not to second guess mike, but we would have similar problems to that so we started wiring ground strait to the battery... With these chasis being 15+ years old and the amounts of rust they tend to accumulate (specially in the radiator suppor) the metal itself may have high resistance from where you are grouding it to the batter, so just rule out any issue, and run the ground strait to the batter and run a good 30amp relay with keyed power from the batter, if your using the Felx-a-lite thermostatic controller, just throw it away, those like to go bad alot