1991 Silverado Gen IV Swap Electrical Help

So I recently got someone else's project for a good price. The biggest issue I'm running into is wiring. They swapped the OG motor to a gen IV 454 with a built NV3500 trans. If anyone can point me to schematics, guides, or how to properly wire this engine swap it would be greatly appreciated.
A few of the issues are:
-spliced wires all over the place, in cab and in engine bay
-none of the gauges worked, and the two that did (speedo and gas gauge), were unreliable at best
-harnesses disconnected in trans area, cab area, and in engine bay
I was able to drive it fine, but just want to undo all the mess and do it right. Not interested in swapping anything out (trans, engine).

What's a "built NV3500"? I didn't think manuals could really be changed much, if at all?

There is a thread someplace on the board that has links to downloadable factory manuals, and they would have the schematics.

You might buy a new (used) wiring harness and start fresh.

That I'm not sure of, I can tell from a lack of an inspection cover that the flywheel is new, and the gearing is far tighter than normal from what I've experienced on other manual chevy transmissions. I have to drop the trans anyway to install that inspection plate and install a seal that's leaking on the tail end of the transmission. I have heard of all-data, but all the places I have looked you have to pay 60 bucks for any schematics. The problem is I would need to do that twice, once for the truck as it is stock, and another for the engine itself. I recently got a Haynes manual, and they haven't let me down yet when it comes to their diagrams. I checked the closest salvage yard for harnesses and came up dry. I'll try out a new one every weekend until I can find one that has something I can use.

454cid said:

What's a "built NV3500"? I didn't think manuals could really be changed much, if at all?

Click to expand...

In general you could get different synchro materials, straight gears, dog gears, cryo treated parts. I don't know what's available for a NV3500 though.

The internals are good, i have most of the wiring sorted out. I am about to start the process of correctly routing and fixing all the wiring.