If it comes on with the a/c, then it's not the fan itself or the ground. I would look at the CCRM module...that's what controls it's various featurs...do a search...I bet more than a few folks have had to replace them. I know I did on my 95. Ford moved them into the pass fender to try to help keep them from heat soaking, but they still fail.
It's just a circuit board with three 40 amp relays on board....common part to have fail.