Tried many different lights, bought a brand new one, all fuses are fine.

 

Did you check the brake pedal switch? What vehicle do you have?

 

I have a 2002 Trailblazer LS. No i didn’t check that switch

 

so the other brake lights do come on? If so then the switch is fine, and you have a broken electrical connection to the high mounted one.

 

Yes the other brake lights come on. What would replacing that entail?

 

Could it be a bad ground? Possibly G201?

 

possibly.

if wiring is bad, then you have to remove the interior trim, find the fault, and repair it

 

Any idea where it could be bad at? I know it’s kind of a dumb question but I need all the help I can get at this point

 

Nope. No idea. But ... it helps to think about what causes wiring faults...

sometimes they break from stress. They get bent back and forth like where doors hinge. (is the brake light mounted to the hatch?). Sometimes they get pinched between two things. Sometimes they get chafed, or rubbed through, like when they're threaded through a hole with sharp edges. Even vibrations can eventually fatigue the copper and cause it to break, especially where wires are loose and haven't been strapped down properly. Hot things can also melt insulation.

Another source of problems is moisture and corrosion. Most of the wire SHOULD be protected by the insulation. So the vulnerable spots are the ends of the wires, connectors, terminals, and sockets where moisture and wick inside and get trapped and eat away at it over time. This is why you will see rubber gaskets inside any connectors that are outside of the cabin. But if water is getting where it shouldn't , then all bets are off. Ground points (where electrical circuits make a connection to the metal of the vehicle body) are problem prone. They get loose or corroded and the electrical connection becomes poor. Your brake light is an exterior feature which is exposed to weather so ...

My advice would be to get wiring diagrams. Most parts stores will have Haynes/Chilton manuals with diagrams. Your brake light won't be a single continuous piece of wire from the brake pedal all the way to the rear. Vehicle wiring is divided into sections to make assembly easier; instrument panel, underhood, doors, headliner, etc. At each junction between sections, the wires need connectors that snap together. That is helpful for troubleshooting, because it gives us a point in the circuit where we can measure, and test, and that helps us to zero in on the problem. Start from the source, the fusebox. See if the circuit is energized there, using a test light, or voltmeter (should be 12V). If it is, move on down the line and test the next point, and so on. I'm betting when you look at the diagram, that the top light will be connected in parallel with the tail lights (that you already know work), which will save you a lot of time.

If you get the fancy 3 inch thick, multi volume service manuals, then they have drawings of where each and little wire is routed, connector is located etc.

You can also buy circuit tracers. You can probably get one at Harbour Fright for twenty bucks. You just clip it on, and you use the magic wand to find wires.



Last piece of advice...
Why did you ask for help in the section that say "This section is not for help threads." in big red letters? All the Trailblazer owners that could actually help you are hanging out in the Trailblazer section of the forum.