Ignition System Wiring Harness - AutoZone Equip cars, trucks & SUVs with Ignition System Wiring Harness from AutoZone. Get Yours Today! We know our parts and products. Automotive Ignition Switches, Wiring Harnesses and Controllers Jun 27, 2015If you don’t have a wiring diagram of your ignition switch handy, the above chart outlines how to use your DMM to determine which wire is which on the back of the switch. The Wiring Harness. Think of the wiring harness as the vehicle’s central nervous system.