I installed a 12V outlet in the bed of my truck this weekend. The wife & I wanted a constant-hot outlet in the truck bed to run a cooler while camping. We have GoalZero solar panels and a charge-controller to keep the battery from draining while out in the woods.
I recommend this mod ONLY if you have a tonneau cover or other means to keep the outlet away from the elements.
For those interested, here's how I did it. It's not the ONLY way to go, but here are the steps I took:
Here are the parts (partially assembled). A Marine-Grade 12V outlet with water-resistant cover, in-line fuse holder with water-resistant cover, ground pigtail wire and supply wire to reach the battery. I used all 12ga stranded wire with a 15amp fuse.
**EDIT** THE LOCATION SHOWN FOR THE FUSE IS NOT THE BEST CHOICE. If doing this yourself, place the fuse as close as possible to the battery, not the outlet. If the insulation on the supply wire gets damaged or worn, the fuse will interrupt the current flow and prevent a short, or worse a fire.
After deciding where to put the outlet, I removed the right tail light to give me access.
Be careful with the attachment clips. The top clip has a red lock that you must slide with a fingernail before removing. The bottom clip has a lock you press while removing.
Here's the 1 1/8" hole in the bed for the outlet. It's wet from cleaning the cutting fluid and chips. I used a step style drill bit.
Here's the hole from the inside. You can also see the small hole for the ground wire, with the paint sanded away to assure a good ground.
Here's a shot of the outlet installed (from inside the tail light pocket). The ground wire is attached and I have easy access to the fuse holder. I can reach the back of the outlet to attach the ring that locks it in place (VERY IMPORTANT). The wiring and fuse holder tuck inside with plenty of room and the supply wire is secured to the tail light leads.
The supply wire follows the tail light leads all the way back to the battery. It is secured with zip-ties every 1-2 feet to prevent rubbing and damage to the insulation jacket.
The supply wire is attached to the + terminal on the battery, supplying a constant-hot lead. The outlet is powered whether the engine is on or not.
Here's the outlet as viewed from the truck bed.
I used a small bit of RTV sealant on the threads of the outlet to keep it in place and prevent the locking ring from vibrating loose over time. I also dabbed some touch-up paint on the bare steel around the hole to prevent rust. The cover built into the outlet is made from soft rubber and forms a gasket on the outside.
I liked the low-profile install look, so I did not use the rectangular cover plate. Also, I did not want to drill additional holes in my truck.
Thanks for looking!