Taillight/brake lights not working properly?

This sounds like a bad ground, or a combination flasher is not working correctly, here is a guide to help you check the grounds and the taillight and brake light wiring diagrams so you can see the ground location and where the combination flasher is located so you can swap it out.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

This guide can help as well:

https://www.2carpros.com/articles/no-tail-lights-exterior-running-lights-tail-lights-out

Check out the images (below). Please let us know what you find.

Hi,

This is a confusing one because power from the brake lamp switch is sent to the lights without interruption.

I attached the schematic below for you so we can work out the issue together.

If you look at the schematic, I highlighted the brake lamp switch. I also highlighted the wiring to the brake lamps. Note the dashed line connecting the wiring. That indicates there is a mechanical connection between the two components.

I have a question. Does the center brake lamp work regardless of the headlamps being on or off?

Let me know. Also, I have a feeling we are going to find an issue with the mechanical connectors, but that is a theory at this point.

Let me know your thoughts and about the center high-mount brake lamp. Also, let me know if the vehicle has an OEM trailer wiring harness.

Take care.

Joe

See pic below.