Maybe its just the video, maybe it's me, but why do the rears look as though they are flashing two red lights and one amber ?
Because they are, lol.
UK Mustangs have different working rears. So under normal operation you have 2 red brake lights and 1 amber flasher. Normall when you press the indicator just the amber flashes slowly. With the cable mod, they sequence red, red, amber unless you press the brake at which point it resume back to standard operation.
It will look better once the rears are tinted red clear.