Wiring diagrams for old cars are different from those of newer cars because newer diagrams obviously reference new parts and systems. Also, new larger diagrams in cars are easier to read, and they use color as part of their legends.
An important difference between wiring diagrams for old and new cars is that diagrams for newer cars refer to parts and systems that have replaced older technology. For instance, old wiring diagrams reference spark plugs while new ones refer to fuel injectors.
In addition, wiring diagrams for older cars are very basic information graphics. Usually they are numbered black-and-white line drawings that refer to a list of parts named at the bottom of the diagram. These diagrams were intended for use by trained mechanics, and often the only way to trace circuitry is with a ruler and a pencil. Fortunately for owners of old cars, drafting companies have redrawn many wiring diagrams for old cars.
On the other hand, wiring diagrams for newer cars are drawn larger so that they’re easier to read. Also, they use colors to isolate parts and systems into groups so that connections are easier to trace across the diagram. For example, if mechanics are working on an ignition system, they looks at the legend to see what color is assigned to the ignition – blue, for instance – then trace the connections to individual components so that they know the whole system.