tjc transport

hi guys, new poster but old trucker here. i ran into an issue with a 2005 CV-713 Granite triaxle dump truck. 427 engine, with eaton fuller 8LL trans. the past few weeks the fan clutch has had a mind of it's own. sometimes it works perfectly, other times it stays locked all day long. it lockup today, and i finally had a test light with me in the truck to do some pinpoint testing. i removed and cleaned the connections on all the fuses and relays in the engine bay fuse compartment, and now have power to both side of alll the fuses. this made the ABS light go out, and the reverse light come on when put in reverse. but the fan stayed locked on. i have 12 volts to the air switch on the firewall, but no ground. the ground for the switch is computer controlled, correct?\does this sound like a bad temp sending unit, or a bad computer? when the fan clutch is working properly, engine temps stay rite around 165 degrees, unless i pull a long hill loaded, then it will creep up to arouns 200 degrees and the clutch locks up. once temps drop to around 180 or so, the clutch unlocks, and if on flats the temps drop back down to 165. oil temps are also around 150-165, unless coolant temp climbs up, then the oil temp rises accordingly. and once the coolant temps drop the oil temps drop also. with the clutch locked up all hte time coolant temps stays around 150 no matter what i am doing. i would really like to resolve this issue, because it sounds like a F-16 driving down the road with the clutch locked up.