Talk about fast relief from wiring pain. Mustangs Plus makes it a cakewalk, with identical factory replacement wiring. A classic Mustang's electrical system consists of four basic areas. The main wiring loom is located behind the dashboard. From the firewall forward is the firewall-to-headlamp loom. For '65-'66, the engine gauge feed runs from the firewall to the engine and starter solenoid. The taillight harness runs from the dashboard to the trunk area. For '67-'68, the story isn't much different. Basics remain the same for '65-'68.