I was still typing about tail lights. Read my post again. I don't have a solution for you on that. I'm not into where you are going. You need a 7 wire turn signal switch. Period. The reason for a 7 wire switch is that it shuts off the brake signal to the bulb/filament that needs to flash. That's what the other 3 wires do.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn