Upper third brake light not working

Hi,

Yes, you can test it with a test light. To help you better understand, the vehicle has a totally integrated power module (TIPM). The power for all three of the brake lights comes from a different pin on the TIPM. If you look at pic 1, you will see three wires highlighted. The two on the right are for the left and right brake light. The one I circled powers the third brake light. Since two of the three lights are working, the fuse isn't the problem. So, either we have a bad ground, the splice in pic 2 is bad and the wire isn't making connection, or the pin in the TIPM that powers that light is bad.

If it is a ground issue, the license plate won't be working either. So check that.

Here is what I need you to do. Remove the third brake light. The connector should have two wires, one is black with a light blue tracer and the other is white with a dark green tracer.

Using your test light, provide a ground for the light and then probe the white/dark green wire for power. Have a helper have his foot on the brake when doing this.

Here is a link that will help you with testing wiring. Although in the link a multi meter is being used, the same principals apply.

https://www.2carpros.com/articles/how-to-check-wiring

Let me know what you find or if you have other questions.

Take care,
Joe

Hi,

That is the brake light switch. Interestingly, if you can get it to work when moving the connector, that must be where the problem is. However, I wouldn't have guessed that. The part you circled is the actuator for the switch. Basically, when you depress the brake pedal, that closes a circuit in the switch and turns the lights on. Basically the same thing as a light switch at home does when you turn the light on and off.

Did you disconnect the connector to inspect it?

Here is the test procedure for the switch itself. It will require the use of a multi meter to check for continuity.

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2008 Jeep Truck Liberty 2WD V6-3.7L
Brake Lamp Switch
Vehicle Sensors and Switches Sensors and Switches - Lighting and Horns Brake Light Switch Testing and Inspection Component Tests and General Diagnostics Brake Lamp Switch Diagnosis and Testing Brake Lamp Switch
BRAKE LAMP SWITCH
BRAKE LAMP SWITCH

WARNING: To avoid serious or fatal injury on vehicles equipped with airbags, disable the Supplemental Restraint System (SRS) before attempting any steering wheel, steering column, airbag, Occupant Classification System (OCS), seat belt tensioner, impact sensor, or instrument panel component diagnosis or service. Disconnect and isolate the battery negative (ground) cable, then wait two minutes for the system capacitor to discharge before performing further diagnosis or service. This is the only sure way to disable the SRS. Failure to take the proper precautions could result in accidental airbag deployment.

CAUTION: Do not remove the brake lamp switch from the mounting bracket. The self-adjusting switch plunger is a one time only feature. If the switch is removed from the mounting bracket, it MUST be replaced with a new switch.

Pic 1

1. Disconnect and isolate the battery negative cable.
2. Disconnect the wire harness connector from the brake lamp switch.
3. Using an ohmmeter, perform the continuity tests at the terminal pins (1) in the brake lamp switch connector receptacle as shown in the Brake Lamp Switch Tests table.

Pic 2

4. If the switch fails any of the continuity tests, replace the ineffective brake lamp switch as required.

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Let me know if you are comfortable performing that test.

Joe