The boat originally had a 454 MPI and is now carbed so there's a lot of extraneous wiring not being used, and I'm also having issues with the dash switches not going to where they should, I'm getting a *pop* through the stereo when I use the tabs, and my trim buttons work sporadically if at all, but the pump is fine. The po sort of fancied himself as capable to work on boats but his work has proven otherwise, and it's 20 years old so it would just be nice to have it all sorted out. Where does one even start?

Ayuh,.... The motors interface with the hull at the cannon plug, so that's not the case,....

As for the other issues, treat each as it's own,....

The poppin' in the tunes is probably bad groundin' somewhere,....
Sort out the switches,...

Boat wirin' ain't that complicated, but completely rewirin' a hull is a HUGE job,...

So you want to rewire the entire huh???

buy a new 10 pin harness of the aprop.. length for each motor. That will take care of ignition and gauges for each motor. buy a new trim harness for each driveand each k plane. get a lot of adhesive.shrink tube connectors, google "boat wiring color coding" and it will give you colors for pumps, lights blowers etc... then buy a lot of wire, decide on fuses or breakers and get quality stuff like blue seas,,,,,

Get a big piece of paper and colored markers and plan everything out then plan everything out again to see what you forgot. buy good strippers and crimpers, not the $5.99 bin ones.

Take your time and plan ahead.

So...it looks like I can get a fresh harness from the cannon plug back, and it's better to work with what I've got up at the switches? It seems like there's no retrofit harnesses or whatnot for boats and if you want all new than bust out the soldering iron a month out of life to do so.

I bought raw wire and built up a custom harness for my restoration.
Not hard and better than slicing and dicing your way through the job.

Start at the helm and work your way back.
Here's a pic of the helm:

You can see the harness on the side here. Used spiral wrap to bundle the harness. There is a. Harness that goes forward and one that goes to the engine room:

You can see the harness's in this pic:

Also be careful when bundling everything all together...think about future changes.

In my infinite wisdom I ziptied everything to the steering cable then stuffed it thru the rigging tube. That worked great until I went to convert to full hydraulic steering and needed to pull the steering cable out.....

What brand stripper crimpers you guys liking?