Same as what everyone else said. 10 ga wire, 40 amp relay, 40 amp resettable circuit breaker, and a switch.
Run the heavy wire from your battery to your fuse/circuit breaker, to your relay, to your light. Run another heavy wire from the black wire to the ground on your vehicle. Next, run another, standard gage wire from the battery, to a 5 amp fuse, to the switch, to the relay and then to the ground. When you turn on the switch, it powers the relay, which connects the power for the light.
Any questions? See the pic of the circuit I wired up.