Scagwildcat

Hi all. Im in need of a little advice,i purchased a 96 gt the previous owner spun a bearing and put in a lower mileage 80k 98 4.6 from a mustang.. he told me that it ran hot! I got the car and had to straighten out some issues with it. I have it running perfect now.. he had constant vac to the egr.. anyway.. ive replaced the water pump. Both temp sensor and sendor figured it was not reading right because of the yeat difference,so i bought aftermarket.. did change anything.. but made my temp guage stick.. so i bought ford oem.. not here's where it gets difficult, the low speed fan works if i unplug the temp sensor.. the high speed fan turns on at 208.4 (normal) my low speed doesnt turn on at all unless i unplug it... i changed the temp sendor with the ford part, turns out the plug is different,so i must have a 98 motor harnesses? So back to get 96 sendor .... ive also replaced the ccrm thinking it was a bad relay. (Ford part) didnt help.... so is my problem the pcm? If so can i just plug in a 98 pcm and have it all work? The fan turns on when the gauge is on the A of NORMAL.. however no matter what i do except unplugging the temp sensor ,i cant get the low speed fan to work like it should.. so in conclusion.. 96.car. 98 motor.. motor harnesses must.be from 98. And pcm i believe is original to the car. Thanks for your help. Ive researched all i can. And cant figure this thing out..