Maybe time to remove all wiring and start with a fresh aftermarket wiring harness!?
Or remove all bad connections and solder them and put some heat shrink wrap on.
For the alternator and wiring ,get a alternator with intern regulator or connect a regulator on the alternator you have.
For a schematic diagram have a look on the www , there is plenty of information to choose from.
Don't know if the 12 valve Cummins still has a electronic shut off solenoid!?
If it has one , remove it and make it a manually shut off mechanism.
Jeep "because mother nature hates flat roads to"
99' Dodge ram 2500 4x4 crew cab 5.9 Cummins ,backup work truck for now
73' Jeep J4000 (named Heep or Desert Dragon) amc 360 V8 converted to LPG with T15/D20 (was my daily work truck for thirteen years and is going to have major overhaul
80' Jeep cj5 350 V8 Chevy/ms420/D300 (a slow ongoing never finished project)
Trucks/car's from the past:
85' Volkswagen caddy mk1 1.6 diesel.
83 Toyota land cruiser BJ42 3.4 diesel.