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Understanding electrical schematics is the baseline. Then wiring is like hydraulics, just pipe the electrons where they need to go. Wiring a complete street going car is mostly tedious labor, coupled with copious amounts of cuts, scratches and muscle cramps. Always best to buy vs reinventing the wheel. Creating a wiring harness for an application means curves, bends and routing concerns, each of these issues creates a different length wire for the bend and getting it right is an exercise in 3D modeling. Then getting wires with the right color codes so your schematic makes sense. Good luck!