I am installing a new flatbed I just built on my 2004 quad cab. My question is how to tye in to the lighting system. I was going to cut the plug off that went toi each tail light. But when I test the wires to figure out what they do it isn't very clear. Two show continuity to ground. When try to find say the turn signal I think I was getting 12 volts all the time on one pin and 9 volts on the other two. Any ideas any one, I need to get these wired properly. I am going to ty into my fourway trailer plug for now so I have brke and tail but I am sure this will cause the lamp out light on my dash to be on at all times.