I decided to draw up a wiring diagram for those that are interested in adding reverse light to your rig. This is how I see it when I look at it. I'm sure it can be done many other ways, but mine works perfect. I used 14ga for everything and 2-40amp relays. 30's are fine. i just had 2 40's lying around. Just a standard automotive relay, whatever is convenient and cheaper. A 10amp fuse should be installed as well for 35/55w lights.
Now, the lights will only come on when the headlights are on which is why I wired it like this to avoid the reverse lights being wasted during the day. Chances are that your not going to need the lights when your headlights are on.
As for the reverse light wire. Mine is an '08 and mine was the white/green stripe and was located under the hood and on the driverside towards the firewall. I used a T-tap and put dielectric grese in it before i squeezed it over the wire. The headlight switch on my H13 socket was white/dark Blue stripe. I wanted to keep the splicing under the hood instead of putting it out in the weather underneath the truck somewhere. You can certainly access any of the wires from the rear, but I'm a corrosion freak. I use all heat shrink connectors and I squeeze some dielectric grease before I heat them up. Then just wipe off the excess. I fished the power wire for the light through the stock convoluted tubing. What a PIA. i did have to use zipties when i went behind the gas tank. No flopping wires. Keep them secure so they don't chafe.
I grounded each light individually to the bed frame. figure 12" wire for the ground leads. I used a self tapper as the metal is thinner there. i squirt some dielectirc grease over the whole screw and around the base. give it a good coating. It'll stay on there for longer than you would realize unless your pressure washing it directly???
It helps keep the screw terminal from rusting and having issue's with the lights later on.
I also peeled the rubber boot back on the backside of the forglights I used and swuirted more dielectric grease all in there. That tire will be kicking up a lot of water and snow. I wanted to make sure they had no issue's. Just another reason if your buying lights to get sealed housings like tractor lights.