First off it sounds like you have some corrosion in your wires, not getting enough current to supply all the lights or just a bad ground, second an aluminum trailer is not a very good ground to start with, do yourself a favor, put a ground buss on the tongue and run the ground from you truck to it, then run a ground from every light to that buss, the trailer places sell a wire kit for this, it's alittle work but once it's done say good bye to most if not all your light problems down the road, I'm going on three years since I did this to mine and I swear by it.