Auto Electrical Diagnostics and Repair

19/04/2022

Common car electrical troubleshooting and repair guide for today’s technician or DIY. 

A light bulb powered by a battery illustrates the 3-Things that all 12-volt electrical circuits must have to operate — Power, a Load Device, and Ground Return. While this may seem obvious, locating the 3-Things, plus whatever controls the circuit, is not as simple as ABC.

Experience has taught us that component location using service manuals and testing their functionality using circuit diagrams makes diagnosis a breeze, except if you don’t understand the fundamentals.

Every electrical circuit on an automobile should have 3 things to operate: 1) a power source, 2) a load device and 3) a ground return. The charging system and battery function as power sources and are extended throughout the entire car by way of numerous wires. Load devices are simply anything that does electrical work and can include lighting, starter motor, onboard computers, relays, power windows, keyless entry, and many other components. The ground return completes the electrical path from the battery-positive terminal to the load device and back to the battery negative terminal. If any of the 3 things are missing, the circuit won’t operate. Wiring diagrams provide a “map” to assist in determining which of the three is not present.

In addition to the 3 things, load devices must be protected & controlled. For protection its must always be a fuse or Positive coefficient thermistor. These are meant to protect the circuit against the excess current. 

As for controls, it's either done using a relay or directly from the ECM/PCM.  The relays and PCM are fused into the circuit to turn on/off the Load, by switching either the ground or power side of the Load. Always watch out for any protective or controlling devices in a circuit.

The process of figuring out how a load device is controlled or protected can be determined once again using a wiring diagram. Find out more about how to fix individual car electrical circuits by following the links below. We will hammer more into the above component's identification and testing procedures. For training purposes on how to diagnose electrical circuits, call us or use the chat button below.