Dim brake lights

Hello,

This could be a corroded ground wire, When any part of the electrical circuit gets corrosion, a frayed wire, etc, this is called unwanted resistance. Electricity has 3 parts to it. Voltage(Electrical force or push), Amperage(Electrical Flow), and Resistance(Anything that opposes the Amperage). According to Ohm's Law, the law's that govern electricity, if you have a constant, which you always do in a vehicle(12VDC)(Battery), then if Resistance goes up, Amperage(Electrical Flow) must go down. This is what is probably going on in your Brake Lamp Circuit.
In the diagrams down below I have Included the Brake Light Wiring Diagram as well as a Ground Distribution Diagram. I have highlighted the two grounds that you should inspect first the make sure they are tight, clean, and making good metal to metal contact. Please check these out and get back to us with what you find out. There are other specific tests to find the problem if these grounds turn out to be okay, so please let us know, either way.

Thanks,
Alex
2CarPros