I have a 2001 jeep Cherokee. Passenger head light does not work at all. Passenger tail light works when tapped on. I can't find the ground wire any where. The only thing I see is the wiring harnesses going from the passenger head light all the way behind the grill which is inaccessible.

 

The tail light ground is behind the spare tire. However, before you go looking for it, check the light itself. If it works when tapped on, your problem is probably in the housing itself, quite possibly the socket. They can go bad, but then, a bad bulb is more likely. Have you tried a new bulb?

As for the headlight, same question. If you have tried a different bulb (swap sides as a test) and it does not work, are you getting power to the socket? How is the continuity to ground? Have you checked?