21. Following the instructions, we moved next to the wiring harness for the new A/C unit. Don't let that jumble of wires fool you, it's super easy to install, and Classic Auto Air provides detailed instructions and wiring diagrams so you can get everything hooked up properly. Critical though is hooking the main power wire for the unit to a key on hot source that can handle the extra draw. Most of the harness is plug-and-play, with only a couple of wires that need to be terminated.