Necessary for all of our LED Bulb Replacement part numbers: LR-57, LA-57, LW-56, LR-56 & LR-67. Needs to be wired into each side/bulb in the bright filament feed wire. Should be placed where heat can dissipate. Outside/underside of vehicle or in trunk area recommended. Can use EL-40 instead if heat is an issue and you would like it to plug directly into fuse panel.