Here's what I did:
I wanted to add some light to the underside of the Jeep and found a vendor on Pirate that was selling little LED light modules that were very compact and waterproof for $35 for a string of 20 light modules. Heres the website:
LED Lights ~ Horse Power Juice! - Rev-X
He sells both the light strands as well as kits which contain the light modules, wire and connectors.
They come as one long string, so you have to cut the wires between each light and splice longer pig tails onto the existing wires. I used the solder pot at work to tin all the leads, since there were 80 individual ends to tin! Since there are two wires coming into each module and two wires exiting, you need to do something with the exiting wires, so I cut them short and covered them with a small piece of heat shrink tubing.
Once that was complete, I soldered the pig tails onto each light and used shrink tubing to insulate the joints. I used 16 gauge wires as these hardly draw any current. I decided to run a parallel circuit with a positive wire and a ground wire, rather than having a bunch of individual grounds to the frame for each light. Obviously, this made it a little more complex, but I didnt like the idea of having all those separate grounds.
The Jeep was wired for factory fog lamps, but the lights were removed when the new bumpers were installed, although the wiring remained. I used those circuits, one on each side of the Jeep to provide power to the rock lights. The factory fog light switch now works the rock lights.
I studied the underside of the Jeep for some time, deciding on the best placement for the light modules. I tried to come up with light placements that would be able to illuminate the ground just in front/behind the wheels, as well as some lighting for critical areas like differentials and driveshafts.
The final placement of the seventeen modules was with three across the front bumper area, two in each front wheel well, one on each side (driver/passenger) on the frame near the front control arm mounts, two on each side tucked up in the tub along the sides where the rock sliders are, one on each side on the frame near the rear control arm mounts and two tucked on the underside of the tub above the rear differential. If you look carefully at the last picture you'll see an in-process picture of my gas tank skid plate that I built.
The light modules were all fastened in place first, using either a #6 x ¾ self-tapping screw through the center hole of the module or using the 3M double stick adhesive that was on the back of the modules. The modules dont weigh anything and the adhesive seemed fairly strong, so I dont really have any concerns about them coming loose.
After they were placed, I ran the supply wires to each light and attached them with a combination of waterproof butt splices and Scotchlock connectors. I know that the Scotchlocks can be problematic at sometimes, but since this wasnt really a mission critical use I decided it would be okay to use them in this application. All the wiring was encased in 3/8 split loom wire and taped up with friction tape.
The main wiring harness ran along the frame rails from front to rear, with the lights being branched off from it along the way. Everything was zip-tied in place to keep it neat and tucked up out of the way.
It took a while to get everything figured out , with regards to location and wiring, but overall a great project that lights up the underside of the Jeep with a brilliant white light. I've got six of the red LED modules, and thinking about adding those inside the cab, for the total UFO effect :)
Heres a few shots of the Jeep, taken in total darkness. The crappy cell phone photos dont really do it justice, as the effect is a very bright, white light that makes the underside of the Jeep bright as day.