There are two filaments in each tail light bulb . One works the stop light one works the tail light. One wire will be powered on only when the brake pedal is depressed, one will be powered on when headlights or park lights are on only. Look at the bulb and you will see the two filaments , one is above the other in the bulb and one should be the dimmer of the two. Verify this by using a meter or a test light on the wires coming into the lights pigtail. find the wire with power with headlights on that is the tail light. verify which wire on your pigtail goes to that filament by turning the headlights on and touching the bare wire from the harness to each separate wire on the pigtail and watching the bulb brightness for each one . The dimmer one is the tail light connect those two. Then connect the other wire to the remaining wire. Test to be sure proper functioning. This is assuming you have a two filament bulb and socket in the light . Should you have a 1156 bulb in a 1157 housing just change the bulb out.