I've got an 04 F150 that I bought used. The compass doesn't work, it just displays two lines under the outside temp reading like this: "--"

Also, the wiring harness that plugs into the rearview mirror is unplugged. I've been reluctant to plug the unit back in because of the crazy stereo system (and other after-market electronics) that also came with the truck.

So, if I plug this thing in right (if possible) will my compass return to normal? What else is controlled by the wiring harness in the mirror?

Thanks

 

yes it should work if plugged back in. it may display "cal" for a while untill it calibrates itself. my guess is the windshield got replaced and they forgot to plug it back in.

 

I think they may have left it unplugged for a reason also. It may short something out, etc.