So I have issues with the break lights, only the rear windshield break light works. I checked bulbs and they're good, does anyone have any clues??

 

I would first check the plug at the end of the wiring harness. Make sure none of the contacts are bent and corroded. Next take a multi meter and make sure you have voltage at the light socket.
If there is no voltage then I would pull and clean the contacts on the SCLM module. It is located underneath the trunk/boot fuse box. Make sure the connections are clean and corrosion free.
I don't think it is the break light switch since the window mounted light works.
Unfortunately the lower break lights go thru the SCLM and it is possible it might be bad.

 

SLCM.
Had exactly the same problem.
Bought a replacement on eBay.
Problem fixed.
Make sure you match up the numbers.

 

+1 get a replacement on eBay. Bunches of threads. Do a Google search. Pay no attention to the YouTube that talks about cross wiring from which ever brake light works: Robert disavowed that approach. It is possible to rewire from the upper brake light; it possible to rebuild the SLCM if you are really good at electronic repair (there is a thread on that approach where Motorcarman (Bob Goff) discussed. If you can wait, there is also an outfit in Idaho that will rebuild and warranty yours for just slightly more than a good one from eBay.

If the SLCM is bad, you will get voltage, but the lights will not work on brake application. Make sure there is no water in the battery compartment under the fuse box where sits the SLCM.

Maybe the administrators can correct spelling errors. Somebody searching for bad Brake lights will never find this thread.

 

Isn't there a discussion about using a trailer feed for the replacement brake light voltage/ground circuit??

 

Yes. They tried this on my XJ8.
It made the lights work, but caused a "check rear light" code every time the brake pedal was pressed.

Told them to put it back and replaced the SLCM and no problems.

I've heard that you can take the board out of an SLCM and put it in the oven for @ 350 degrees for 3 minutes can fix a bad solder connection on the board, which is usually the case when they go bad.