Hi, I'm having problems with my '97 Mercury Mystique. The low speed fan relay refuses to turn on. The car is overheating, but the wiring is okay. I replaced the thermostat, relay, and temperature sensor. I replaced the ECM, but the problem persists. I can get it on if I jumper the ground side of the relay though.

Any ideas what to try next?

Welcome . You may have to change the relay or resistor again.
Read this thread for some help

or do the moderndino fix (only as a last resort).
moderndino fix