I bought my 2000 Mustang with sequential taillights that the previous owner installed. The left and right bulb on my right taillight stopped working and don't work as brake lights or with the blinker on (makes a fast sound like a light is out when I use blinker). I've changed the bulbs and it didn't solve the issue. I took out the light and went over the wiring using AM's sequential taillight instructions. Everything was wired correctly, but I rewired a ground and another wire so they had a better connection. The two lights still do not work with the tails or blinker on, however they DO flash when I lock or unlock the car.
What would be causing this/how do I fix it?

Any help is greatly appreciated!! Thanks!