Hey guys, I have '88 C3500 that I will be re-doing all the wiring etc. I will be using the Speedway 22 circuit wiring kit... https://www.speedwaymotors.com/Speedway-Universal-22-Circuit-Wiring-Harness,229874.html I currently have the digital controlled HVAC system. I was at the 'yard on the weekend and saw that you would also get the older style controls in our trucks. How hard would it be to do this? I would put power to the fan switch. Other than that; the steel wires would have to connect the ductwork etc..I just recall that in my '70 Chevrolet Monte Carlo (before it became a drag car) it wasn't too complicated..