trailer grounding

after seeing smittys post on grounding it reminded me of my grounding trouble on a trailer. have a trailer with a big box. and 14 or 16 lights. with a 4 wire connector. and taking 100 hours putting the lights on, it seemed like. side note here, why on earth some one uses a white wire as a ground wire? anyway, with it hooked to the truck they was not bright enough. so you have 3 16 ga wires going to 14-16 lights. and the white ground ( return ) is 16 ga to. yep you figured it out. so a separate 12 ga wire fixed the trouble. gronding truck frame to the trailer frame, in addtion to the 3 wire setup. the big hint was that a good 6 amp battery charger isolating the truck volts and ground, did not fix the trouble.