You sure it is not the ground? If I remember correctly, which I may not, I think the whole tail light housing is the ground which can cause problems if you switch the style. It has been a year since I did mine so I dont remember 100% As far as the switch, that is on the side of the transmission and can be tested with a wire. The lights themselves are just another fuse.
I'M FLEXY AND I KNOW IT
95 YJ, 2.5 AX15 conversion, 4.0 TB, SOA +1.5", 33" DC Crusher Tires, 8.8 Rear w/welded tubes + LSD, Spartan Locker HP30 Front w/solid axle swap, Rocky Road OTT kit, Safari Snorkel, Warn VR8000 Winch, Smittybuilt front Bumper, JKS Disconnects, AA SYE, Teraflex Shock Bar in Rear, 1/2" Boomerang Shackles, RE Add a Leafs, Homebrew Traction Bar, Monstalined in&out, LED Tail lights, 1700 Watt Stereo