Separate all of the pieces of your spotlight kit. Some kits come with small tools, wires and screws.
Disconnect your car battery. Remember to disconnect the negative terminal first.
Find the wire that has the fuse built into it and strip the end of the wire closest to the fuse. Clamp the terminal connector that came with your kit to your wire.
Connect that same wire to the battery of your car by stripping the other end and wrapping it around the post. Run this wire to the inside of the car to the location where you would like the switch to be mounted. Then connect the wire to the positive prong on the back of the switch. Mount the switch in an easily accessible location.
Run another wire from the ground prong on the switch to an unpainted location on the car's frame.
Attach another wire to the last prong remaining on the switch. Run this wire to the back of the light and attach it to the yellow, white or blue wire coming off the back of your light.
Drill holes in your car that correspond to the spotlight where you would like to mount the spotlight on your car. Normally a spotlight is mounted on the door near the side mirror. Bolt the light to the car using the hardware provided in your kit.
Connect the black wire coming out of the light to another unpainted section of your car's frame to ground it. Reconnect the battery and test the light.