Once you check the voltage like missileman says, try to back track the wiring to see where the voltage break is. This can be a PITA. The headlight switch is a common problem on Wranglers, but very easy to replace. The high beam switch is not too bad to replace. My sons Jeep had a similar problem, turned out to be at the fuse box, where the wire going out from the fuse looked like it was intact but when I pulled on it with needle nose pliers it was loose, had corroded away. Not sure about the Rubicon, but on the Wrangler it is easy enough to get the fuse box off and check underneath.