I have a 2010 Ford Mustang GT with vector v2 aftermarket tail lights and the sequential isn’t working and only the first of the three bars are lighting up tried disconnecting the battery, didn’t work anything helps thanks

 

Make sure the ground wire is connected, and making good contact. It has been years since I installed mine, but if memory serves, there is a separate ground wire that if the connection is lost, the taillight functions like a normal factory light.