More and more problems arise that simply cannot be solved by replacing or repairing individual components such as the idle speed control, air flow sensor, control unit, ignition distributor, etc. The wiring in our buses has been installed for at least 33 years and, especially in the engine compartment, is exposed to significant temperature fluctuations. Corrosion under the insulation and corroded connectors/contacts are commonplace and often difficult to locate. It's easier to replace the entire wiring harness, which will save that area for the next 30 years.