There are typically two wires for each tail light: a positive wire and a negative wire. The positive wire is usually red, while the negative wire is usually black. However, it's important to check your specific vehicle's wiring diagram to be sure.
To determine which wire is which, you can use a multimeter to test for continuity. First, connect the positive lead of the multimeter to the tail light connector. Then, touch the other lead to each of the wires in turn. The wire that registers continuity is the positive wire.
Once you know which wire is which, you can hook up the tail lights according to the manufacturer's instructions. In most cases, the positive wire will be connected to the power source, while the negative wire will be grounded.