There are many parts and pieces when it comes to lights. There’s marker lights, signals, brake lights, headlights, daytime running lights, fog lights, cabin lights and bunk lights. All these lights have different wiring sometimes teeing into each other sometimes they have their own circuit. Fuses, relays, junction boxes, wires, switches and connectors are also part of these circuits. As you may imagine, any of these different components could be the reason your light isn’t working, it’s not always as easy as just replacing a bulb or light (although we wish it was). Without the right schematic in hand or up to date knowledge on these systems it’s hard to make an accurate diagnosis of what is actually causing the light to not work.