Quick parts list update - the fuel line cap with the eBay link is not needed. You can re-use the one that comes on the aux fuel port on the rear tank. I thought the size was different but nope, it works fine. So I edited the post above and crossed it out.
Anyway - the install is going well, it's getting close to done. Should have it done Saturday night or Sunday. I thought I'd start updating with some details and pictures.
Step 1 - Electrical
BIG EDIT: When I started this I was unable to find the rear harness for my truck, and it looked like even if I could order it it would be $500-600. It looks like the part number for a 2022 3500/4500/5500 Chassis Cab with surround cameras is 68525916AB, and it's around $260. So if you want to skip all this and just replace the rear harness, get that and skip to step 2 with the brakes.
I'd start with making the electrical modifications because it doesn't require any Mopar parts, it's "reversible" and if you aren't comfortable with this part you shouldn't try this modification. You'll be rewiring both fuel pumps and fuel senders so you need to do a quality job on the splices, otherwise you'll find yourself stranded sooner or later. This isn't necessarily going to be a step by step, but I'll do my best given a lot of these pictures are of black parts against a black frame rail. I'll try to provide diagrams where I have them.
There are two big connectors in the left side frame rail right about where the tank goes. One has a blue handle (its connector name is XY965A if you want to look it up on Tech Authority) and one has a grey handle (XY960A). We'll need to modify some wires on both of these connectors.
Here's the general overview - all trucks are wired for both tanks up to these connectors. However on the rear side of the connector, if your truck is a rear tank only truck the wires for the midship tank are unpopulated. On top of that, for a rear tank only truck the rear tank is "tank 1", however for a dual tank truck the midship tank is "tank 1" and the rear tank is "tank 2". More details to come on how this all works later when I go over the plumbing changes.
So what this means is not only do we have to provide the wiring for the midship tank, we also need to reverse both the fuel gauge sending unit wiring and the pump wiring so the rear tank becomes the second tank.
I don't have access to whatever type of wiring pins these connectors use, so I don't have the option to rearrange the pins as needed and add the wires/pins to the rear connectors. If you do great, but what I opted to do is cut these particular wires before and after the connector and bypass the XY960A/XY965A big connectors. I made two new connections using Weatherpack connectors that I had on hand. If I were doing this from scratch and didn't already have this stuff I'd probably use some kind of Delphi connector, they're good and easy to obtain. I made the connectors reversible so each tank is on its own weatherpack connector and each uses the same pinout/gender. That way I can swap the tanks between tank 1 and 2 both for testing and maybe in the future if I come up with some jumper fuel lines if the midship tank's fuel pump dies on me.
Whatever you use you'll need enough to make two 3 pin connections, one for each tank. I had some 4 pin weatherpack's so I used those and put the proper plug in the 4th pin.
You'll need to start by carefully removing the fabric and electrical tape from the first few inches on each side of each of the XY960A/XY965A connectors. Be very careful, if you damage a wire you're going to be in a world of hurt. My advice is take the outer wrapping off but leave the inner wire loom and/or cloth covering intact so you can re-use it. In the example below (this is the rear harness disconnected) I peeled back about to where the first zip tie is in this picture.
Once you have all 4 of these cable bundles peeled back, you're going to need to mark the wires you need to cut. I usually mark mine with little bits of blue tape before I start cutting anything.
Blue handle (XY965A) - forward connector:
Pin 7 - Black - Fuel Sender return signal (this is common between both fuel senders)
Pin 8 - Dark Blue with Grey stripe - Fuel sender 2 signal
Pin 22 - Dark Blue with White stripe - Fuel sender 1 signal
Grey handle (XY960A) - forward connector
Pin 19 - Dark Blue with Yellow Stripe - Fuel Pump 2 (aka transfer pump in a dual tank setup)
Pin 25 - Dark Blue with Orange Stripe - Fuel Pump 1
<continued..>
