Check the lights on your trailer or 5th wheel without having to plug into your tow vehicle. Simply plug your 7-pin RV plug into the LIGHTCHECK. The lights on the unit will come on, allowing you to do a walk around and see what's working and what's not. Can test turn signals, brake lights and amber warning light – the LIGHTCHECK will not blink if lights are not working properly. In case of emergency, the SAFETY PLUG feature allows you to leave your rig safely on the side of the road – the LIGHTCHECK and clearance lights will illuminate and the signal lights will blink anywhere from 10-24 hours.