[95 GTS]

there are 2 speeds on the 94-95, the high speed scomes on at 208 degrees or when the a/c is switched on.

a few things could happen. your car is not hot enough at idle... a good thing
your high speed has burned out.... happend to mine but it is ok because i have a big aluminum radiator.
you may have had the recal done which actually SCREWED up my fan and the high sopeed would never come on. when I removed their relay it worked again.
if you haev temp problems you can try the high speed manual switch. I believe you tap the purple and black wire on the ccrm( box on the overflow tank) and wire it to a switch which runs to a 12v source. You can check the wire schematic on stangnet in the 94-95 section.

Hope this helps.