Brake light night mare

I suspect that there is a weak connection in the brake light circuit that is opening up under full (6-bulb) load.
Is this a factory disc brake car? If so, there is a 2-pin jumper from the brake switch to the harness that fails.

Unplug the red connector and apply 12V directly from the battery to the green wire on the controller…
You should get 4 out of the 6 brake light bulbs to light up.

Yes it a disc brake car. I did what you said to do and I indeed got 4 out of 6 to light up.

Well after that you got me into checking wires. Came to realization the green wires on the red connector were backwards!!! I realized the one i had 12v on didn’t go to the one you had me hot wire. Thankyou for all the help. All works now !