[BR3W CITY]

I had a harness built for me (engine side) and it came with the relays and its own little fusebox. I like that it was much smaller, and cleaned up the look alot for where my box has to be mounted (directly on the inner fenderwell, everything is directly accessible).

In some cases, I'd also consider what we did on the body side. You end up pulling out so many engine wires, that the old body harness starts to look "hollow"...since you've cut some of the wires, looms etc. In my case, the body wiring had been modified before, a common story. This means random radio wires, splices-on-splices, and colors going everywhere.
We decided that it was worth it just to gut the thing, and re-wire the hole truck ground up. It sounds daunting, and we had the help of an industrial wiring rack and a 35year master wiring tech.....but that actually makes it sound worse. With a simple approach, anyone can do it. We simplified the whole thing, and allowed room for our new gauges, stereo etc. It all went to a simple 12-slot fuse block, mounted on the firewall in the cab. Makes troubleshooting easier, and my wiring diagram is a simple printout from PhotoShop.