Brake lights don’t light
Diagnose brake lights don’t light
If your brake lights don’t light, the problem can be as simple as burned out bulbs, a fuse, bad brake switch or a bad ground. Here’s how to diagnose the system.
Brake light switch wiring diagram
Every car maker wires their brake light switch and lights a bit differently, but this diagram is fairly common.
Power flows from the fuse to the brake light switch. Once the brake pedal is depressed, power flows through the brake light switch to the high mount brake light and the right and left brake light. The lighting circuit terminates at a single or multiple ground connections.
On some vehicles, the brake light switch is also the trigger for the ABS controller and the shift interlock solenoid. The shift interlock solenoid prevents you from shifting out of park without depressing the brake pedal. In this diagram, the brake pedal switch provides power to the shift interlock solenoid, but in other wiring setups, the shift interlock switch is powered from the ignition switch and the brake light switch provide the ground path to activate the solenoid.
In some other setups, the brake light power must flow through the hazard warning switch.
In still some other setups, the high mount brake light switch is powered by a separate fuse. The resoning behind that is that you would still have some brake light if the main fuse blew.
Using a meter to test your brake lights and brake light switch
Set your multimeter to DC volts
The brake light system is “hot at all times,” meaning you don’t have to have the key turned to the RUN position.
Connect the black lead of the meter to ground. Using the red lead, touch each terminal on the brake light fuse. You should see battery voltage on both. If so, proceed to the next step.
Locate the brake light switch under the dash on the driver’s side. Back probe the brake light switch. You should see battery voltage at the switch. If so, depress the brake pedal. You should see the voltage drop to near zero. If the voltage remains at battery voltage, you may have burned out bulbs or an open in the wiring.
Remove the brake light bulbs from the socket. With the brake pedal depressed (parking lights OFF), probe the terminals inside the socket. You should see battery voltage on at least one terminal.
Troubleshoot other brake light problems
As I said at the beginning, car makers wire their brake light systems differently. If your tests don’t show the same results I’ve listed here, you may have a different setup. In that case. see these other posts for helpful information
©, 2019 Rick MuscoplatPosted on by Rick Muscoplat