Electrical Basics and Automotive Grounding Systems

By Vince Illi (AKA Dusty_Duster)

I’m weird.  You see, most car guys don’t like electrical work.  In fact, most loathe it.  (A friend of mine once told me he’d rather replace a head gasket than crimp four wires together.)  But me, I like electrical work.  I would rather rewire an entire dashboard than remove an intake manifold.

Automotive electrical systems really aren’t that difficult, though.  Everything in a car other than the alternator and electrical sensors operates on Direct Current (DC).  That means that the vast majority of anything you do on a car is governed by only two laws.  (If you’ve already got a good  grasp of electrical theory, feel free to skip the next part.)

Electrical Basics

Ohm’s Law states that the current through a resistor is proportional to the voltage across it.  Here’s Ohm’s Law:

V = I R

In simpler language: the voltage (V) across a resistor is the current (I) through the resistor multiplied by the resistance (R).  Here’s a simple circuit diagram to illustrate this:

The symbol on the left is a battery, or a source of voltage.  Since this is a car, we’ll just assume it’s 12 Volts.  The current (I) flows through the resistor (R), also known as the load.  Think of a battery as a pump.  It exerts a pressure (the voltage) on electrons, making them move.  The rate at which these electrons are moving is the current.  A resistance to that flow is the resistance (R).  Most things connected to your vehicle’s electrical system can be thought of as resistors.

The higher the resistance, the lower the current.  The lower the resistance, the higher the current.

See, that’s not so bad, is it?

### 1 comment

1. Tony J says:

Very good read. I would just add a word of caution when tieing Electrical Ground to Signal Ground especially in newer vehicles with more onboard electronics. The Electrical Ground provides the voltage differential to insure things like Spark Plugs work well. However, spark plugs (and wires) also generate lots of signal noise that electronics do not fair well with.