Thats the fun part, you either have to pay someone to figure it out or just screw with it and do it. As long as you have a fuse you wont screw something up, just blow a couple fuses. Grab some resistors, try wiring them in different spots until it works. Maybe there is something on google you could find with resistors and where to wire them for a smaller amperage light fixture on a 12 volt system.