Check whats backfeeding the coil positive. If its the cooling fan then check its circuit and if its tied to the same leg of the key switch you will need to either install a fan relay to control the cooling fan or install a HD diode like you see on some cars to isolate the cooling fan from the ac compressor clutch.
Diode to allow power to go out from key but not come back to key. My memory on khyber is a bit rusty but I think it has such a system in place, it maybe bypassed by ustaads in the past.