VFT,
I'm not sure why you have four wires going to the back unless you have backup lights or else the extra wire is for the fuel gauge. Normally, there is one wire going to the back which splits and goes to each taillight filament and one wire each for the turn/brakelight filaments. Use a multimeter set to volts and operate the turn signal switch to determine which is the turn/brakelight wire for each side. Turn the parking lights on to determine which is/are the taillight wire(s). The fourth wire, if it is not for a taillight, will either be a fuel gauge wire or a backup light wire. The way the correct turn signal switch works is that the brake light switch is wired to the turn signal and the turn signal interrupts the brake light signal on the side to which you are turning and flashes the light on that side and allows the brake light to work normally on the other side.
