Inside the truck is a large collection of Lighthouse Bulbs. The majority of them are damaged with the exception of one. Acquire it, then head back to the Lighthouse. Atop the Lighthouse, walk up to the mechanism and Activate to place the working bulb. Hit the electrical switch on the wall, and the lighthouse is lit... a beautiful sight.
The lighthouse's rotating projector contains two broken lamps. During the quest, you replace only one of these lamps. There is no way of replacing the second one, even by adding another lamp to your inventory via additem console command. You can't even replace one lamp if you have two or more of them in the inventory.
Sometime after your first visit (not necessarily after you've lit the lighthouse), six Smugglers have taken up residence, filling the tower with lots of loot. One guards the outside entrance; if you fast-travel there while crouched in Chinese Stealth Armor you teleport right in front of him and can dole out a sneak critical. Four more smugglers are positioned inside along the spiral staircase; the one at the (inside) top has a missile launcher. Near the top of the lighthouse, outside and to the right, is the last smuggler. Further to the right beneath the stairs is another missile launcher and 10 missiles.
In all, the newly-inhabited tower contains 6 ammo boxes (many are missile-heavy, one is average-locked) and 5 first aid boxes (many are stimpack-heavy, one is average locked). You'll also find a table covered in caps and a Stealth Boy. Besides the missile launchers and other smaller gear, the smugglers are armed with 2 sniper rifles, a Power Fist and 4 sets of combat armor.
NOTE: Smugglers, and thus the ammo cache, may never appear at the lighthouse. (Confirmed Xbox 360)
