Wiring Harness Turn Signal/Brake Lights

I installed an universal wiring harness from Painless in my 67 GTO. Everything seems to work fine except the tail lights when I am using the brakes and a turn sinal at the same time. The brake lights and the turn signals work fine on their own. When I have a turn signal on, the brake lights do not work. The turn signals seem to override the brakes - in other words, If the brake lights are on and I flip on a turn signal, both brake lights will turn off in favor of the single blinking light.

Has anyone experienced this problem? Am I missing some sort of jumper wire that the directions failed to mention? Are there any sort of tests I can preform to find the problem? Thanks in advance.

Welcome to the board petegis. I have to ask this question, have you called the Painless folks? I believe they have a technical support. They are the ones who would know which wires may be crossed to cause that problem.

Good luck with it

Pat