How to Troubleshoot a Rear Brake Light

Written by jonra springs
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How to Troubleshoot a Rear Brake Light

A driver is responsible for all legal requirements of a car on a public road. If the brake lights aren't working, a police officer may stop the car and issue a warning to make the repair within a given time limit. Before that happens, troubleshoot a rear brake light yourself and possibly save on auto repair. It can be simple to discover why stepping on the brake pedal doesn't make the bulb light. Fixing the problem may only require common parts available at chemists, grocery stores and auto parts chains. Otherwise, the wiring may have to be checked throughout the circuit.

Skill level:
Moderately Challenging

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Things you need

  • Owners manual
  • Vehicle assembly manual
  • Phillips head screwdriver or star key wrench set
  • Possible replacement bulb and/or fuse
  • Voltage tester
  • Extra wire (12 to 20 inch length)

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  1. 1

    Check the display. Ask a helper to step on the brake pedal while you check the lights from the rear. If no lights appear, check the fuse that connects the brake lights. The owners manual will show the location of the fuse box and which fuse is for the brake lights. Pull out the fuse and look at the wire in the central window. If the wire is broken, replace the fuse. Make sure the new fuse is not blown, and carries the same amperage.

  2. 2

    Take note of lights that are out, if any are working. The problem may be cured by replacing the bulb in a brake light that's out. A burnt out bulb has a broken filament and a dark brown spot on one side. Check the owners manual for bulb type.

  3. 3

    Check the circuit if replacement bulbs and fuses do not restore the lights. Find the wiring diagram in the vehicle assembly manual. The circuit for the brake lights runs from the battery to the fuse, to the pedal switch, to a connection plug, to the lights. The circuit has to be checked with a volt tester at all points.

  4. 4

    Check the battery power and the light on your volt tester. Turn the ignition key far enough to activate the electrical systems. Turn on the lights to check for battery power. If the battery has power, ues it to check the volt tester. Put the black lead (the ground) from the volt tester on the negative battery terminal. Briefly touch the red tester light on the positive terminal. The light on the volt tester should flash brightly.

  5. 5

    Test the wiring to the fuse. Clip the ground wire to solid metal near the fuse. Touch the light tip to both sides of the fuse. Both should light the tester. If neither side lights, the wire between the battery and fuse is bad. If only one side lights, the fuse is blown.

  6. 6

    Test the switch and wiring. Touch the light tip of the tester to both terminals on the brake pedal switch without putting any pressure on the pedal. One should carry power and the other should not. When both show power, the switch is stuck and the brake lights are always on. If neither shows power, the wiring between the fuse and the switch is bad. Now check both switch terminals while the pedal is depressed. Both sides should light the tester. If not, the switch is bad.

  7. 7

    Check the connection plug. Unplug the connection and refer to the vehicle manual to identify the brake light wire. Touch the tester light on the brake light wire at the inner socket on the battery side. If the tester lights, the power is flowing to this point. If not, the wire between the plug and the pedal switch is bad.

  8. 8

    Check the socket. Plug in the connector plug and remove the bulb. Touch the contact inside the socket. If the tester lights, the socket is good. The socket and wire running to the plug should be replaced if the tester doesn't light.

  9. 9

    Check the bulb with the ground wire. The bulb must be in its socket. The ground wire running to the socket should be black or brown. Stab the tester through the insulation. If the tester lights, the bulb is good. Replace the bulb if it doesn't light.

  10. 10

    Check the ground wire. Remove some of the insulation around the ground wire. Twist one end of the extra wire around the exposed ground wire. Touch the other end to a solid piece of metal. If the brake light comes on, the ground wire is bad.

Tips and warnings

  • Do not attempt steps 3 through 10 unless you have experience with auto electric wiring.

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