uses a direct connection to the tow vehicle’s battery to power the trailer’s stop, turn, tail and running lights without overloading the vehicle’s electrical system. use when: trailer has more than 1 light assembly per side and is equipped with multiple clearance or running lights; if tow vehicle may tow a variety of trailers; if tow vehicle has ‘lamp out’ sensors. re-settable short circuit/overload protection – guards itself and the tow vehicle from shorts and wiring install mishaps; rated at up to 4.2 amps for turn/stop circuits, 7.5 amps for taillight circuit. for vehicles with pulse width modulation (pwm) taillights, ensuring full brightness of the trailer lights; use on 2 or 3 wire systems; works with led and/or incandescent bulbs (vehicle & trailer). Fit type: Vehicle Specific.