Is this easy to replace? It is very dim and sometimes doesn't even go on when I'm braking. The tail lights are fine, just the long light in the rear window.

 

Replace the 3rd brake light. It's an LED unit.

 

is it possible to just replace the brake light switch and that fixes the problem?

 

I was told that I needed a new third brake light by a dealer on this past Friday. ($130). I found on here that it was possibly the brake light switch. ($13). I installed a new brake light switch and and it fixed the problem!! Try it first and see if it solves your problem.

 

It's more than likely the brake light switch. Very common issue.

 

Mojofo, is it a new switch I need to get for the third brake light? And how do I replace the switch? And where can I get a replacement. Chop, chop!

 

yeah, 3rd brake light switch behind the brake pedal. Easy DIY.