Yup...FSM with wiring diagrams,a multimeter,lots of patience and beer.
In this case,what I had done the past is a total gut and start from scratch.
If the harness is beyond repair score a good used harness,perform continuity tests on all circuits,repair whatever needs repairing and re-install in the car.
I also unwrap the harness check for damage and re-wrap it so it looks clean and no spagetti mess hanging at your feet.
Now is the time to bypass the bulkhead for the main red and black wires that feed the whole system AND do an ammeter bypass/shunt under the hood.
With the dash already out install an electronic 5 volt limiter for the gauges-worth the extra cost and no headaches down the road (literally)
I solder and shrink tube any broken wires but never the main feeds.I replace the wires stem to stern
Pull out and Clean up each and every spade in the bulkhead connector.
Labor intensive but never have to do it again.
Clean each and every ground in the dash and under the hood.
Best of luck and any ?? PM me.. I love and hate electrical in our beloved Mopars,LOL!!