Find out the power needed for the 2 bulbs, amps or watts.
Make sure the bulbs and the truck are the same voltage.
You don't need to use a relay unless you really want to. You can buy a switch rated for more than the required amps and go direct with the correct gauge wire.
If you want to use the relay, make sure it is rated higher than the draw of the bulbs or you are just adding another weak link.
The relay will have 2 poles for the contacts to switch the lights and 2 poles for the coil to activate the relay.
Power from the fuse for the lights to one side of the contacts, wire to the lights from the other side of the contacts.
Power from a fuse to one side of the switch, other side of the switch to one side of the relay coil. Other side of the relay coil to ground.
Easier to just buy a correctly rated switch and wire from the light fuse through the switch to the lights.
Use heavy enough wire.
