What junction box did you replace for this?

And it's an electrical circuit. It's not enough for the bulb to just be getting power, it also needs to get a connection to ground. You might take it apart again and check for that.

 

I Replaced The Rear Junction Box As The Tail Light Bulbs Were Dim . Replaced That And The All Lights In The Tail Lights Are Now Okay . I Only Checked For Voltage Because The Previous LED 3rd Brake Light Worked And Then Went Dim Out Of No Where . I Just Figured That The LED’s Finally Went Out . I’ll Double Check My Ground . The LED That I Bought Only Has Pins For Power And Ground . I’m Pretty Sure That’s My Problem Because I Dont Have A Signal Wire From The Connector To The Brake Light .

 

And some led's need to be connected to power and ground on specific pins to light up, others can be connected either way.

 

LEDs in CHMSLs tend to be a problem in some GM vehicles that did not have them ad OE. Put incandescent bulbs back in and I'll bet it works fine.

 

I Would’ve Put In Incandescent Bulbs To Begin With But The Previous Brake Light Had A Full LED Circuit Board . There Wasn’t Any Bulbs . So I Figured A Plug And Play One Should’ve Been Fine . But If All Else Fails, I’ll Just Install The OEM One And Move On With Life

 

Some led lights have special circuitry so the two pins to the light can be connected either way to power and ground. But some cheaper lights don't have that circuitry, and need to be plugged in a specfic way, so a specific pin gets power and the other pin gets ground.

It would not surprise me if your original led still works fine, and it's a connector or ground problem.

 

I’m Still Going To Double Check The Ground And Power To The Light . I Did Get This Brake Light From Amazon So I Wouldnt Be Surprised If The Signal Wires Wouldnt Be Wired Into The Power And Ground .