Lean burn removal

Oh and it appears to me that someone has already turned that harness into a rats nest.
My 85 d150 was absolutely THE worst in that department when I first got it. I'm surprised it hadn't caught fire at some point before I got it and
so I felt that I had to take care of that issue.
Mine was hacked so bad that I went to the junkyard and got a different harness, and started with that instead. The one I got was from a 1 ton V8 truck so in essence the lean burn delete was already done, could have been simply plug n play, as I unhooked the wiring from the bulkhead and plugged in the replacement. But I went farther.

I did have to extend a few wires, not bad at all.
I did untaped the replacement harness and went thru every inch, I did find some spots where insulation was chipped, etc from sheer age and heat cycles... I fixed those, replaced a couple of sections of wire, while at it.
What I also did was to go back to the junkyard and got an underhood fuse box from a different vehicle and wired that in, deleting all of the fusible links at the same time.
I had a factory service manual spread out right along side of me the whole way.
I have somewhere a TSB from the Littelfuse company that tells of the development of "maxi fuses" and how they were developed specifically to replace fusible links/ and used that for much of my ambition for the modified harness that I created.
There are countless possibilities there but for my purposes as I walked the junkyard I settled on an underhood fuse box from a 90-92 ranger to incorporate into my truck. I wanted something small and compact with enough fuse holes for my needs. This application has I think 12 fuse slots, and depends on how fancy the truck you pick the box from can have anywhere from 8 to all 12 fuse slots "hot", while leaving some slots as "dummy blanks".
I looked til I found one with as many live fuse slots as I could. I have a few unused but that's ok as id rather have that than to not have enough. That gives me room in case I want to add things later.
I also added a 2nd, redundant 10 ga "hot" off the back of the alternator, thru one of the "extra" fuse slots and then straight to the battery. When you get into that harness you'll see why.
At the back of the valve cover, there's a black plug where the actual engine harness connects to the rest of the underhood harness, and all the potential juice from the alternator ran thru 1 blade type terminal, and then splits 4 ways about 1 ft from the battery into 4 fusible links which are much smaller gauge but power up most of the truck. I put each of those 4 on their own circuits, plus now have a direct line from the alt to the battery, besides. While it would be crazy overkill to do so it don't hurt to have "too big" of wire gauge from point a to point b, but you can definitely have "too small" .
I know this goes beyond what most are wanting to do to their vehicles but it's the best way (that I know of anyway) to eliminate alot of problems these trucks came to be known for over the years.