A standard relay is good for about 30 amps. At 55w each light will draw about 4.6A each, so conservatively we will say 5A each is the draw. A maximum of 6 lights can be powered from a standard relay. The relay is used to switch the power properly. Most stitches, even if they say they are rated for that much power, are crappy and can easily melt or break and short out on or near the mounting surface. Another purpose for this it to not have to bring the power all the way to the switch and through the firewall and all. The "high power" side of the replay can remain in a safer place than inside the cab. Look up various size charts for the length and draw you will have and the proper size. 8-10 Ga wire should be sufficient, but I doubt that it is speaker wire like you previously stated. I would run at least 10ga wire, I did that for my air compressor for my horns. Properly fuse the system and wiring the relays and such and you will be fine. Sounds like you have a little more reading to do.
Why do you need so many lights under the truck?
2003 Ranger supercab XLT 2wd 4.0 auto - sold
2004 F-150 supercab FX4 4wd 5.4 auto all black and silver leather interior...rockin' the fullsize