I went out to my 89 Cherokee this morning and it started as usual, but when attempting to back out of my garage, I was unable to get it out of park as the shift interlock wouldn't disengage. I started investigating to see as to what else might not be operating and found that the headlights, brake lights, emergency flashers, and tail lights wouldn't come on. The high beam will not engage the lights by clicking or holding it into position. The dome, reverse lamps, and turn signal lights come on normally. I've checked all fuses (even with a meter) and they're good. I've just replaced the headlight switch, but have the same issue, any ideas?

 

Okay, it looks as though there are 2 separate problems. Given the down time, I decided to put in a new ignition switch that I'd had purchased a while back and now I am able to take it out of park. I still have the lighting problem, so I broke down and bought a Haynes manual and armed with my multimeter I am going to try to shoot some wires. It looks as though all the main lights are powered through the headlamp switch via a red fused wire.... more to come.

 

I was going to say headlamp switch anyhow - had a similar problem in my 87, and have seen the same problem in a number of vehicles.

Make sure the Big Red Wire(tm) is getting power - if it is, replace the switch. If it's not, check fusible links (I think there's one devoted to feeding lighting, but don't quote me on that) and fuses (which, I believe, are downstream of the switch. Again, don't hold me to it...)