I added lots of lights to the Beast, my '86 GMC Dually. I bought some Hella Rally 4000 lights with the conering beam pattern (flood with top cutoff), some worklights for the sides and rear, and mounted them on a custom lightbar. At the center is a multi-mode amber LED emergency strobe, an Able "Show-Me" unit. It has about 350 5 mm LEDs, is very bright, and works well. It originally had magnetic feet but I permanently mounted it to the light bar. To fabricate the lightbar, I used a perforated 1 X 1" steel tube mounted to the roll bar, and wrapped it in diamond plate alum as a wireway. The wires enter the roll bar at the top, and exit the rollbar end through the stake pocket of the bed, and into a box I made from the same alum. The box houses the relays and fuses. It was a bear pulling all those wires through the rollbar.
I bought many many automotive LED light accessories on ebay. One item was an LED underbody kit (white LEDs), that I mounted under the bed rails as cargo lighting. In this picture I don't have the tonneau cover yet, but with it on it's pitch black under there without the lights.
The lights are controlled by a switch panel I made from textured plastic sheet. I can control the forward and rearward pairs of lights, the LED strobe, and left or right worklights individually. Toggle switches at left control the cargo lights and running board lights and select the mode of operation (on, off, door switched, park light).
The truck originally had no dome light at all, and there was no light available to see anything inside while you're driving. I took a clue from the German cars and installed some red LED cockpit lights. These were originally LED wiper arm lights (pretty stupid IMO) and had a set screw clamp. I cut off the clamp part, modified them a bit, and used 4 of them on the headliner (actually there's no "liner"). They can swivel and point which is nice. I wired them to a toggle switch that selects on, off, or park light activated.
I also bought an actual BMW dome light unit on ebay, with two red LEDs built-in as well as 3 switched bulbs. The curvature didn't work with my roof, and I also had no storage, so I fabricated a fiberglass roof cubby that has storage at the rear, and the BMW dome light at the front. I made a skeleton from alum mesh, built it up with figerglass strips, and finished off with body filler. It was a royal PITA.
At the rear of the roof I mounted 2 LED light bars to serve as the main dome lights. Here's some pics looking up at the roof from the driver's side:
Here's some detail of the cockpit lights, one above the driver's vent window, and the 2 center-mounted:
I also mounted 4 amber LED bars to the underside of the hood to serve as service lights. They are supplemented by a period Chevy truck reel light - a magnet-backed bulb housing attached to a 20' retractable wire.
Here's a picture with the lights on. There are 3 red LED bars rear-facing under the roll bar. These operate only with the brake and turn. All 3 light for braking, and the left and right flash with the blinkers. There are 3 more red LED bars under the tailgate that are running or park lights. These red LED bars are Eurolite brand and are highly recommended. They have selectable output (park/brake), aluminum end caps (aimable), and braided SS wiring. The other brands used for the dome and service lights are not as durable. Also note the LED SS exhaust tips behind each rear wheel.
One challenge was to get the running board lights to operate as I wanted - that is to come on with the door switch when you entered the vehicle, and also with the parking lights. The problem was that the door switch is a switched ground, and the park lights are switched positive. I had to use 2 relays to isolate the circuits from backfeeding each other.
I also installed 2 switches for the cargo lights. One in the cab, and one at the tailgate so either can turn them on or off.
I learned a lot about auto wiring working on this truck, and pulled many hundreds of feet of wire and loom. I was working on it very consistently for at least 6 months.
Here is what I have on my mustang:
