One thing none of us Catalina owners like are those damn trailer plugs...Looks like a 27' with the engine location and your avatar pic??
One piece at a time dude, and you'll get it back in order. Those spark plugs need to be replaced and plus 1 on the dizzy cap and rotor. You can get all that stuff here at MMI or we can also cross reference some parts to places like a local NAPA.
My gauge pod on my 30 looked like yours. I replaced the entire thing from the panel to the engine with direct runs and no plugs in the middle. There is a Blue Seas junction on the bulkhead. You can see that in the engine pic..it just takes a little time!!
One thing we can discuss down the road is some of us have eliminated the Ammeter up in the panel, because of the long run of the alternator wire. I put a simple volt meter in its place..if I see 14-ish volts I know the alt is working..don't need Amps in the panel.