12V DC Wiring
Above is a diagram of my 12 volt wiring as it is right now in 2020. I have made several changes over the years. For one, I've installed an inverter and smart charger, both of which require heavy gauge wiring to the house batteries. Both of these are physically located under the second row passenger-side seat. I removed the original low-end charger/converter that was located under the rear drivers-side bed.
I have protected both positive take-offs from the batteries with class T-fuses. These should ideally be within 18 inches of the battery, but I had to mount mine a little further due to space constraints. One of these is positioned in the space under the toilet, and the other is attached to a rear bumper mounting bracket, under the back of the van. I bolted the fuses directly to the cable lugs rather than use a dedicated fuse holder to save space, and protected both of these fuses using plumbing parts to build small enclosures.
I also installed cutoff switches to both positive battery lines. This enables me to effectively isolate the batteries from the rest of the system if I need to work on the 12V system or when I put my van in storage. This will guarantee that there is no current draw on the batteries. I used Blue Sea Systems Mini Battery Switches, which are rated at 300 Amps. The Blue Sea products that I've purchased are of very high quality.
Overview of electrical compartment located under the drivers-side rear bed.
Electrical compartment under drivers-side rear bed. Here you can see the red 12V cut-off switch I installed on the right. In the middle is a relay (BatteryLink ACR) that is able to disconnect the van alternators charging line. I am no longer using this and leave it connected all the time. On the left is the Intellitec Relay that can shut off the power to the 12V distribution panel when you press the button located over the passenger side door.