What do I need and what do I don’t!
I have a 1975 scamp 318 backed with a 904, I am running my ignition system with a MSD 6A box, that being said nothing really electrical works on the interior of my car except the radio.
So some of the this may be self-inflicted?
The '75 A-body splits the power on the engine compartment side, So its not like earlier models. If you didn't know that then this where you need to begin. Study the power feeds so you know where they go.
My question is what wiring under the hood can I get rid of and what do I need to keep? The original wiring harness is hacked up and basicly junk!
The power circuit must be kept. Follow the wiring from the power supplies (battery and alternator) using the diagrams and comparing with routing on the car.
The ignition circuits must be kept. One is for ignition start, and the other one, connected through the 1/2 ohm ballast runs the ignition, alternator field, and any other engine relkated doodads that were added such as electric choke, idle stop solenoids, etc.
I have aftermarket fuel, tach, oil gauges. I really just want to clean the wiring up and not have such a rats nest!
In addition or instead of?
You can draw power from the switched power buss of the fusebox if there is a place to piggyback or add an additional fuse.
To light the gages, take from the instrument light circuit. You may be able find an unused connected if there were originally options for consoles or such.
Its really important to route and bundle the wires with good support, and allowance for strain relief at each connector. Study the factory wire routing and support.
In the engine bay, use wire that has insulation rated for heat and oil.
Good terminal connections use terminals that support both the conductor and the insulations.