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:

Simple Circuit
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?

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Thursday, December 09, 2010 7:09 PM
Good stuff. Like many high school kids, the first thing I modded on my car was the stereo system. I remember when the first grounding kits came out, I laughed at how expensive they were. Just go buy car audio stuff!
Thursday, December 09, 2010 10:53 PM
my hyper voltage regulator grounding system is worth $200, right?

Thursday, December 09, 2010 10:55 PM
Thursday, December 09, 2010 10:58 PM
Or should I have spent my money on a giant tach?
Friday, December 10, 2010 2:53 AM
Neat article, very well written. Glad to see MotoIQ is opening the doors for other guys to contribute. Looks like I'll need to do some crimping over winter on my 240.
yo vanilla
yo vanillalink
Friday, December 10, 2010 4:24 AM
I can run and splice wires fine, but I can't read a meter and therefore can't diagnose electrical problems as well as I'd like (though as a previous old VW owner I've managed to get around the block once or twice)

Look forward to more!
Friday, December 10, 2010 4:49 AM
Good starting article. I'm looking forward to more advanced articles that can help me put a modern fuse/relay box in my "classic" car. I understand how to read diagrams and how electricals work, but a complete rewire with mixed components seems to be a challenge.
Dusty Duster
Dusty Dusterlink
Friday, December 10, 2010 4:53 AM
Check Summit Racing Equipment. They have several universal kits for rewiring old cars. These kits include fuse boxes and relays. I believe the brand name is Painless Wiring.

If you need to rewire just the engine bay, look at some of the universal wiring harnesses offered by MegaSquirt.
Friday, December 10, 2010 9:37 AM
Nice article I can't wait for the next one.
Friday, December 10, 2010 10:44 AM
@ Dusty
I'm too cheap for Painless kits. They do offer some great features, but this is more of a "junk yard" project like many MotoIQ and Dave Coleman inspired projects.
Friday, December 10, 2010 1:29 PM
I was preaching grounding kits on Turbododge 8 years ago but no one believed me. Grounds are the key especially on 80's or early 90's cars.
Friday, December 10, 2010 3:18 PM
I personally do grounding kits on cars more for safety than anything. MR2's were one of the first cars I started hot rodding seriously and every year you hear about one guy's MR2 that had bad engine grounds and caught fire. Throttle cables and aux grounds will glow red hot, melt fuel lines, then you know what comes next....

If they are doing anything for power then that is just a bonus. I would say most of the empirical evidence leads us to believe that at worst they do nothing, at best they can give you a couple of ponies.
Saturday, December 11, 2010 9:53 AM
They probably don't make any power, however it makes it run like it was when it was "new"
Monday, December 13, 2010 8:27 AM
Very cool, I appreciate the good newbie info to get the series started. The cheapy grounding fix might be useful for my 94 Ranger. Looking forward to the next articles that detail how to troubleshoot and fix electrical problems. Like why does my truck's rpm meter only sporadically work? Or why doesn't that LED dash light work anymore? Keep it up!!
Tuesday, February 17, 2015 1:47 PM
This was really informative. I have been wanting to learn more about the inner workings of my car, including the electrical system. The more I know, the more I can keep track of things and know when to take my car in for maintenance.

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