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This week's "Gadget Freak" article from Design News shows you how to build your own trailer light hookup - "Trailer rental firms insist that tow vehicles provide operating lights -- turn, tail and brake lights for every towed vehicle rented. Easy to do if the tow vehicle is wired that way, but a pain if it has separate turn and stop lamp circuits. John's solution is a pair of diodes, some quick disconnects and an inexpensive wiring harness. He used Schottky diodes for low- voltage drop, rated 3A to handle 36W of trailer lights. He then threw in a few quick splice connects for the rear tail light wires and the mate to the trailer's 4-Way Flat and was set quicker than he could say "You haul!" Oh, yeah -- be sure the vehicle and tow hitch can handle the trailer, cargo and tongue weight." - Link.