Skip to main content
November 27, 2023

Importance of wiring diagrams

Imagine that you have a car come in with an intermittent fault, say an occasional cut-out, and the car has already been to one or more other workshops with no success. The customer, who is rapidly losing faith in the garage trade, just wants it fixed. What do you do?

You’ll probably start by having a look over the vehicle to see if there is anything obvious or missing, then you’ll likely plug in your scan tool. Assuming that neither of these checks yield any useful results it is probably time to start delving into the diagnostic process a little deeper and reach for a wiring diagram.

But before you can do that, you’ll need to know exactly what a wiring diagram is, and how to read it.

Understand the meaning

Simply put, a wiring diagram is a visual representation of an electrical circuit. The distance between points on the diagram don’t literally show the tangle of wires on a vehicle, but following a trace on the illustration will exactly represent the way that components on a vehicle’s electrical system are laid out.

Up until the end of the last century, diagrams were only available in physical service manuals which even on a simple car from the 1980s could mean you tracing the line with your finger over several pages. It was easy to lose track of the connection you were tracing, and the fact that these diagrams were not typically printed in colour didn’t help.

Computers changed this. In the 1990s it was possible to consult full wiring diagrams on monitor screens, albeit usually on bulky hardware in the front office using software running from physical discs. Later, laptops and tablets as well as cloud-based software such as Autodata with full colour, interactive diagrams made tracing faults even easier.

Users can now search for components, zoom in and out at will and click through to related sections and other relevant information.

Labour intensive process

Each diagram is produced by the in-house team of automotive technicians and technical illustrators and is based on OE data. Drawing such diagrams and making them accurate is a highly skilled process and very labour intensive and often involves negotiations over copyright with the vehicle manufacturer, but as they are so vital to technicians, Autodata allocates significant resources to their production.

This modern way of presenting the data is most welcome. Apart from the sheer number of diagrams for every model of vehicle (There can be as many as 30 separate diagrams for each model, and Autodata currently has 290,000 <CHECK> and counting on its system), each reference has scores of control modules, sensors, hidden fuses and earthing points that will need to be found and tested while checking a circuit.

Experienced technicians will, as a bare minimum, have a test light and a digital multimeter to test for power, bad grounds and check components. Other commonly used tools include a device such as a probe that supplies 12v (or 24v) to load circuits with voltage in order to test them, and oscilloscopes that let technicians ‘see’ what is happening in a circuit by clamping on to the wires and producing a waveform, of which a snapshot can be taken and studied to reveal anomalies.

 “Modern electrical systems and wiring harnesses are becoming increasingly complex and even the most experienced technicians can find repairs daunting without assistance” said Salim Arkadan, Principal Product Manager at Autodata.

“Our continually expanding library of searchable, interactive colour wiring diagrams helps those automotive professionals with their diagnostic process and trace the fault quickly, every time,” he added.

Share this article: