Most things originate from under the dash, as previously mentioned push under dash wires thru from engine compartment, route toward each component. Cutting the old wires with 6-12 inch left makes routing and finding easier. I started with a bare cab using Centech harness/fuse panel, they print on their wire the destination, I'm sure others would also, makes for easy quick job. I found the Chevy gauges were easier to wire in place. Zeke
