what is the issue with the wiring?
I would start by downloading and printing the wiring diagrams found here.
https://67-72chevytrucks.com/vboard/...d.php?t=185856
That will help identify which wires you need to look for to solve problems.
If it's all hacked up, you may want to consider a new harness.
You can get separate harness components such as the engine harness and front lamp harness
that will plug right into the bulkhead connector at the fire wall and replace all the hacked up wiring under the hood.