I've notice that my odometer on my '02 mustang has been going on and off at anytime. I started to see this when my car reached 90K. I also have a '99 F-150 that stared when it reached 90K also now has 102k. Has anyone else had this problem with any mustangs out there?
Check the ground behind the center console. It is shared by a number of devices including the radio, GEM, cluster, ODB2 port. It's frequently messed up during a radio install.
Follow the multiple black wires from the radio is one way to find the ground.
Another option is to test the ground wires at the cluster connector. Look for the black wires and the black wires with a white stripe. Again best to use a test light that will "load" the circuit.
Note, testing a ground with a VOM may work if the ground is open. However the VOM method want be able to tell a good ground from a "weak" ground. Again the best method is to use a test light that will apply a measured "load" to the circuit.