Indeed, one of those wires at the center feeds license lamp, the other feeds the Fuel tank sending unit. Both of these items then ground to the body. As for color, just look at a wiring diagram to see which is which...or turn the lights on to see which one goes hot with the lights.

Are you installing a NEW harness? Or re-hacking the old one? The only real "clips" were little plastic push-pins that snap into round holes at various places along the bottom of the taillamp support panels. If you bought a new harness, these clips should be wrapped within the taped wires, and in about the right places, allowing you to easily see which hole each clip aligns with.