I want to replace 6 hardwired 20W 12v under cabinet lights with LED 4W 12v lights. First one replaced fine but when replaced 2 more, lights started flickering. New lights have 1 red wire and 1 black. Wires from wall are red and white. I was doing red with red and black with white. All lights are controlled by one switch. Some lights have 2 sets of wires coming from wall. Any thoughts?