Ya, that kit wires you up like a boat trailer which works fine until the Jeep brakes are pressed, because the Jeep brakes energize the light whether the MH does or not and it over-rides the MH flashing signal.
All of these kits cause complications. I went with this one from Hopkins
Hopkins Jeep WranglerIt uses diodes and just intercepts the wiring to your tailights. If the MH is hooked up, the Jeep is working off the MH pigtail. The downside is, the side running lights on the front fenders are not powered from the running lights, only the rear, and kind of a unique aspect is the 3rd brakelight doesn't come on with MH braking, but does when the auxiliary brake in the Jeep activates. I kind of use that to my advantage as it alerts those in the rear of some extra braking going on rather than just my stupid federally mandated brake lights coming on with the exhaust brake...all the way down the pass :)