An electrical power supply device for a trailer lighting system behind a truck is disclosed. The trailer lighting system including at least two FMVSS 108 compliant LED stop-tail-turn lamps. The electrical power supply device has an outer casing including a terminal to be electrically attached to and become part of the trailer lighting system. There are a plurality of electrically conductive wires within the casing. At least one of the wires is selected from one or more of the group consisting of low copper usage wire. The device has an over-current protection device along at least one which breaks current flow through the one wire below at an amperage threshold less than 25 amperes.