Connecting to the Brake Light Wiring Circuit
If you've determined the problem is with the brake light switch or with the wiring, then you'll need to know about connecting to the brake light wiring circuit. The circuit is essentially the full run of wires from the battery to the fuse block, from the fuse block to the brake light switch and then from the switch to the brake lights themselves. Sometimes, the wires may also run to the body controller. Most of the wiring is bundled in a wiring harness that runs through the entire car.
If your brake repair requires you to connect the brake light switch to the circuit, start at the fuse block. Find the hot side of the fuse block and run a power wire either from the terminal for the brake light fuse or from another hot pin on the block. This wire should lead to the brake light switch. The switch itself is connected to a plug, so you may need to splice your power wire to the power wire coming out of the plug. Once the switch has power, you need to connect the output wire from the switch to the rest of the brake light wiring harness. A wiring diagram for your specific vehicle will show you which wire in the bundle to splice. As long as you're taking a careful approach, chances are that you shouldn't need to replace or rewire entire sections of the brake light wiring circuit — just find the faulty wire, section of wire or component.
Let's find out more about the brake light switch on the next page.