The top row is the number of amps applied to the wire. Choose a column that is equal to or greater than the maximum current draw of your light bar. The intersection between the selected row and column indicates the proper size of wire, in AWG or American Wire Gauge, you should use for the circuit. It never hurts to choose one gauge larger, which means a lower AWG. This provides a greater margin of safety. When wiring LED light bar relays or switches, fuse all positive side wires such as from the positive battery terminal to the light bar switch.
Most light fixtures have two electrical wires with colored insulation and a copper ground wire. An enthusiastic homeowner can save the cost of a professional by knowing which wires connect to which. With this knowledge, you or a family member can do the wiring connections for one or more lights. Turn off the electrical breaker for the circuit to the existing light fixture. If the breakers aren't labeled, ask a family member to turn on the light with the switch as you cycle through the breakers until it goes off.