1999 Lincoln Continental cooling fans

My 1999 cooling fans stay on all the time. I bought the car that way, mistake. I have checked the relays, they work fine. I was on a trip and started smelling something burning. I pulled over and found a fire in the pass side cooling fan. I had to pour washer fluid on the motor to put it out. I unplugged the fans so it wouldn't happen again. I have replaced the fans but it will wear these out to if I don't find out why the fans won't cycle like they are supposed to. Any feedback would help. Thx