How Do I Test a Brake Light Switch?

The brake light system on any vehicle will contain some type of an electrical switch which turns on the brake light when the brake pedal is depressed. Like any switch, it can go bad causing the brake lights to not illuminate. If none of the brake lights on a vehicle light up when applying the brake, there is a good chance that the brake light switch is defective. Testing this switch is one step in troubleshooting brake light problems.

Testing a Brake Light Switch

Step 1 Look under the dash and locate the brake light switch near the top of the brake pedal. Usually, this switch is attached by means of a bracket to the arm of the pedal with two wires attached to it.

Step 2 Look at the wires attached to the switch and verify that they are securely attached to the switch. A loose wire will cause the switch to not activate the brake lights.

Step 3 Examine the alignment of the switch and verify that the plunger on the switch activates when the brake pedal is depressed. A switch that is out of alignment will not activate the plunger and therefore fail to turn on the brake lights.

Touch the positive lead of the tester to one of the wires on the switch, with the other lead of the tester touched to bare metal. If the test light illuminates (or volt meter reads 12 volts), then you have located the feed wire for the brake switch. Move the positive lead to the other wire on the switch. The test light should not come on (or volt meter show no voltage). With the leads in place, depress the brake pedal. The test light should illuminate (or volt meter read 12 volts) if the brake switch is operating properly. Otherwise, the switch is defective and should be replaced. If neither procedure light up the test light (or reads 12 volts on the volt meter), then the brake switch is not receiving power and the problem is in the wiring to the switch.

Things You'll Need: 12 volt test light, or voltmeter