Most conventional vehicles use a 12 volt negative grounding system. Many of the cars and trucks today use many different computers, modules, relays, switches, sensors, wiring harnesses, etc. to control and monitor vehicle systems. Computers are used to control everything from engine management, emissions, ABS, Airbags, lighting, audio, windows, doors, and so on.
Testing electrical circuits is a very important part of vehicle diagnostics in todays cars and trucks. Most all systems on todays vehicles are electronically and computer controlled.
A good solid knowledge of OHMS LAW is needed to understand how to diagnoseelectrical circuits and understand the results of the testing.
Improper testing can cause more damage to a system than the original problem. Intermittent problems are the hardest to repair and require a Techician who is very familiar with whatever vehicle he / she is working on. Experience is extremely important. Vehicles change from year to year and model to model.