The lucky owners might only have 4 damaged wires. So colour matching and doing 1 at a time removes a problem waiting to bite. I have seen these with wires melted together creating wild electrical faults like only able to turn the car off by turning the light on! This along with the ignition switches and corroded earthing points have often been the route of troubles and it is easy to look. I think the design idea for this generation was to keep the wiring dry by having it above the exhaust. Add 30+ years and you also get hard and crunchy wiring going into the box as most cars have long ago lost the exhaust manifold heat shield that connected to the airbox for winter running.
