Maybe the person u bought it from jumped the fans to be on at all time when the ignition is on. The fan relays are in the ccrm which is inside the fender for the passenger side. Could be a relay shorted but i would start looking for some shady mechanic work just my 2¢. Also if it was rigged up like that may wanna look into a bigger problem i.e overheating issue.
1996 Mustang GT, 17x9 front and 17x10.5 cobra r replica rims, 255/40/17 front 285/40/17 rear at the moment,
o/r x-pipe flow master 40 series dump downs, cai/ram intake, 75mm c&l throttle body and plenum, pi heads and intake swap, msd wires, stock gears, untuned at the moment, no dyno numbers for now.