3rd brake light on while driving

[gilbertvial]

I have a 1995 RS coupe, I've been told and noticed that when my lights are on my 3rd brake light is on as well, even if the brakes are not pushed. If you push you brake, the 3rd light gets a little brighter but I'm sure it's not very noticeable while driving. Any thoughts on what could be the issue?

 

[Merlins Beard]

My guess is that the 3rd brake light was re-wired at some point and for some reason, probably for a spoiler. The wiring when it was re-done was not done correctly and the person that did it wired it up to the low output wires on the main brake lights. The main lights use a bi-filament bulb, one for low output when the lights are on, and one for high output when braking. The 3rd brake light is likely wired to the low output set of wires.

 

[phatintegra]

There is a brake pedal switch. It's located behind the brake pedal that need to be replace.