There’s an emergency medical technician (EMT) axiom that states:
Air goes in and out.
Blood goes around and around.
Any deviation from this is not good.
Electricity, as in the direct current that now controls more and more of vehicles and machinery, also goes around and around.
For example, the headlights on a tractor or pickup or car.
(A bit of nomenclature here. When a water valve is closed, the flow of water is stopped. When a water valve is open, water – or whatever is in the pipeline – will freely flow through. When an electrical switch is open, no current can flow through it. When it is closed, the connection is made, and electricity may flow through the circuit. An “open” circuit means there’s a break or disruption in the wiring, so electricity will not flow through.)
The circuit through the headlight starts at the positive post of the battery. From there, the wiring goes to the switch. Opening the switch disrupts or stops the flow of electricity, turning the headlight off. From the switch, the wire runs to one side of the socket for the light bulb or element. The electrical current does its work as it flows through the filament or diodes of the light bulb. The wire from the other side of the socket returns the electrical current either via a dedicated wire or through the frame of the vehicle or machine.
Most vehicles and equipment are negative ground. Some, usually vintage vehicles, were (and are) positive ground. If in doubt, follow where the wires from the battery anodes or terminal posts run. Generally, a wire will connect directly to the vehicle frame from the negative post if it’s a negative-ground vehicle or from the positive post for the rarer positive-ground rigs.
As the electrical current flows through the light bulb or element, the resistance to the flowing current heats the light element (in an incandescent or halogen bulb) or energizes the diodes (as in a light-emitting diode – LED – light).
Now comes the part that takes a bit to get one’s mind around. Look at a standard (non-LED) light bulb. Look at the tiny coil that gets white hot, producing the light when it’s energized. Now compare the size of the filaments in that tiny coil with the size of the wire that feeds electricity to the unit. The same electrical current that makes that element glow white hot flows through the copper wire feeding it without that wire getting hot. Why? Resistance, measured as ohms. (Named after a German, if I remember correctly, physicist named Ohm.) The larger copper wire feeding the light socket has very little resistance to the flow of the electric current through it and gains no heat in the process. A greater charge of electricity requires a larger copper wire to let the electricity pass through without raising the wire’s temperature.
The metal in that filament is specially formulated to tolerate being repeatedly heated and cooled between times of being turned on and off. The size of the filament and its length and makeup determine the amount of light it emits.
After the “work” of illuminating the light bulb, the current completes its circle, and through a dedicated wire or the frame or body of the machine or vehicle, it makes its way to the negative anode (post) of the battery.
Electricity flows in many ways, as water or other fluids flow, and is referred to as an electrical current, like a current of water. Like water, electrical currents follows the path of least resistance. After doing its work of overcoming the resistance, or ohms, of the light fixture or other device, the least resistant way back to the battery is via the ground wire or through the grounded frame of the machine.
Electrical currents are very persistent. If the route for the return current is compromised – a connection is broken, corroded or simply loose – things can literally go haywire. The easiest situation to diagnose and repair is when there is a complete break in the path of the returning current.
Consider a marker light on a trailer: one hot wire feeding the light and a ground wire attached to the vehicle frame. If that ground wire corrodes through or its anchor point breaks clean, then the light simply will not work.
When the symptom of an electrical upset is something weird – like when you step on the brakes, and in addition to the brake lights coming on, half the marker lights also come on – check the ground wires first. What’s happening is that the ground to the brake lights is compromised, and the easiest way back to the negative battery post is by back feeding via the grounding to the marker lights. Often the lighting cord for a long trailer will ground to the frame at the front and also at the rear, with some of the lights grounding directly to the ground wire within that main cord.
Another symptom is when the brake lights or turn signals only function correctly when the taillights or marker lights are turned on. For your information, I have personally replaced the entire main light cord on a 40-foot hay trailer, only to have the same gremlins still exist. The five clearance lights across the rear were all grounded to the same spot on the frame via a connector that looked robust. Having replaced and rewired everything else on the trailer and being to the point of dynamite therapy for the trailer, I took that connecting bolt out to find compromising corrosion and rust that was not visible before taking it apart. Then all the lights worked perfectly.
Now, entering the world of computerized everything
An appliance repair technician told me that my new washing machine was not a computerized washing machine. He said, “It’s a computer washing your clothes for you.”
It’s wonderful when it works. When a ground connection is compromised and it’s a sensor that tells the computer that operates the engine on your car or pickup that’s involved – the possibilities are amazing.
When the instrument panel on a vehicle or machine appears to have analog gauges, but you remove it to troubleshoot and find it to be totally computerized, and the results posted via analog pointers – it’s a whole new world.
As an example, the tachometer on my 2006 pickup started giving obviously wrong engine rpm readings. I asked the online gurus; the consensus was a cold solder joint that frequently stopped flowing the correct mini ohms for the beast to work and display the correct rpms.
Troubleshooting parts of a computerized system, you will note that the ohms to test components are very small compared to bigger parts of the system. That translates to a compromised ground to any part of the system being able to wreak a similar havoc to the system as the earlier example of the trailer lights.
This will help to explain why an automobile that has been even partially immersed in water, especially salt ocean water, can became a pariah on the used car market.
