heres info on troublshooting shorts in 90 cherokee.

[gorman90xj]

if your taillights, parking lights and gauge lights are out heres a way to finding a short. first check the switch, and the fuse in the parking lights inlet (10 amp). if the fuse keeps blowing you have an obvious short somewhere, the problem is where. in the rear there is your back valence that covers your rear speakers and ect. behind the valence is your speaker wires, license plate light, rear window defroster and wiper. the thing that goes out the most in 80's and 90's xj laredo's is the license plate light, which is a gray and blue wire, there is a fusible link (3 i think) that burn up very easily....it is connected to the parking light fuse inlet which controlls exterior lights and gauge lights, if there is no license plate wires touching each other then it is not the cause of the short, take off the two rear inside panels were the spare tire is mounted and plug in a 30 amp fuse in the parking lights inlet, pull the light switch all the way back and feel the wires that run through the panells in the rear for heat, your tailights and ect. run through here, trace the wires that feel warm and look carefully for touching wires....hope this helps.