i had the same problem with my old fox
it turned out that some of the copper wire was exposed where it hooked up to the fan and was causing all sorts of problems. it could very well be something of the like. i burned out 2 30 amp relays in a week.
i changed the way i routed the fan wires and cleaned it up a bit and problem solved. i still have a new relay, high quality at the house. i was using the discount auto brand also, but a local race shop that isnt a sponser gave me the one that worked for 2 years, and he gave me two. if you want it its yours, dont know if you are willing to drive to palm harbor to get it, doubt it but its good stuff. ill be back in tampa off fowler next week, doubt you can wait but it saves you a drive

. but a relay should be a relay, but i swear it made a difference
keep in mind the fox i had didnt have a electric fan to begin with, and i was the one who wired it up. at first i had it so the fan turned on by a switch, i honestly dont recommend it wired up the way for a daily. took a bit of gettng used to to remember, and if anyone else drove the car i had to keep reminding them to turn it on. so i made it so the fan would turn on by igintion switch, but took forever to warm up. should have done it temp sensor wise, would have been much better
you might want to bite the bullet and wire it up that way, id be willing too if all the shit you have tried is still failing. maybe bypass the issue that you are having, but it still wont fully resolve the problem of course.
just my .02