I am refurbishing a 1988 TT and cannot figure out what is wrong with the 12v lights. I checked the battery, and it is fine. I ran a long jumper wire from the ground on the battery to my test light and I have power at the socket in the 12v light, but the bulb will not come on in any of the 12v fixtures. I even tried a new bulb to be sure, but nothing. This has me thinking I have a ground problem, but, then again, the water pump functions normally. There is only one ground wire hooked to the battery, so it has to be the same ground feeding the lights, right? Also, when I touch the test light to either the end of the bulb in the fixture, or the side casing, my test light comes on. I thought the side casing of the bulb is for the ground, but I'm not sure. Any suggestions?