Check your ground. Make sure the white wire is making good contact to the frame on both vehicles. If in doubt, take a pair of jumper cables and go between the frames. Or take a meter on the 20 volt dc scale, hook the positive to the Jeep and the negative to the tow vehicle, any voltage at all tells you no ground, it is trying to ground through the meter. You can do the same with a test light, if it lights, no ground.
Hope this helps