There's probably no other factor that causes more vehicle
problems than poor electrical connections. From slow cranking engines to
poor sounding audio systems, electricity, or more exactly the lack of
electricity may be at fault.
While we commonly use the word electricity to describe power, it can be
better described and understood if we talk in terms of voltage, amperage and
resistance. This is easier than it sounds, so stay with me. Let's start with
voltage.
Think of voltage as simply a push. Provide voltage to a completed electrical
circuit and it will push the electrons along the wires. We can have voltage
without anything happening. For example, our automobiles have 12-volt
batteries but until we connect that battery to the electrical system by
turning the key, the voltage does nothing. The higher the voltage, the more
push is provided, and if the voltage is high enough such as lightning or at
the spark plugs, it can even jump through the air.
Amperage, often called just amps, is the flow of electrons. Amperage does
the work in an electrical circuit. On a car, the starter motor may use 400
or more amps when it is cranking a cold engine. The heater fan can use 15
amps, while a rear window defogger may consume 20 amps. As long as there is
voltage applied to a complete circuit, the amps will flow easily through the
conductors but add resistance in the wrong places and the amps will stop
flowing.
In simple terms, resistance opposes flow. Just as a mud puddle slows a
vehicle, electrical resistance slows the flow of amps. There are places in
the vehicle where we need resistance. A light bulb has a high resistance
filament inside that heats up when amps try to flow through it. A windshield
wiper motor uses resistance to limit the maximum speed it will operate at.
Solenoids, motors, bulbs and relays all have resistance in them and that is
good. There are also places where resistance is bad.
Resistance can occur in any part of an electrical circuit. It could be at
the battery, the power wire, switches or the ground connection. Ground on
modern vehicles is the circuit back to the negative post of the battery.
Often, the vehicle's body and frame supply the path for the ground
connection. The most common places for high resistance are where there are
connections.
Poor ground connections are the most difficult resistance to diagnose. A
poor ground will cause the amps to flow back to the battery through the next
easiest path. This can be through other electrical circuits and it can cause
several devices to malfunction at once. Whenever I work on a vehicle with
multiple electrical problems or strange malfunctions, the first place I
start is to clean and tighten all the ground connections.
You can find ground connections anywhere on the body but there are usually
several in the engine compartment and on the engine. Look for a wire bolted
to the vehicle's body or frame. Remove the bolt, clean any corrosion or
paint from under the wire terminal and bolt it back to the body. Also clean
the negative battery cable where it bolts onto the engine or frame and the
ground strap from the engine to the body. These simple steps may fix many
electrical gremlins.
Let's take a look at some common electrical faults. Electric fuel pumps need
to generate the proper fuel pressure for good starting and driveability. If
the pressure is low, the vehicle may hesitate, stall, or even not start.
Testing fuel pressure is easy enough, but when the pressure is low, the fuel
pump is usually replaced, however, a poor ground reduces the flow of amps,
and the pump doesn't run as fast. Fuel pressure will be low. Some of these
pumps cost hundreds of dollars so before replacing one, clean the ground
connection for the pump motor.
New sound system not performing right? Perhaps there is too much resistance
in the system's power wires. The more amps that flow to a device and the
further it is away from the battery, the bigger the wire needs to be to
allow the amps to flow. For example, a 1000 watt stereo (and there are many
out there!) needs a 6 gauge (.162 inch diameter) wire to handle the flow or
there will be resistance in the circuit when maximum flow is needed.
Experienced technicians will use meters to measure the voltage in different
parts of an electrical circuit to determine if there is excessive
resistance. At home, many problems can be prevented by cleaning and
tightening electrical ground connections.
Jim Kerr is a master automotive mechanic and teaches automotive technology.
He has been writing automotive articles for fifteen years for newspapers and
magazines in Canada and the United States, and is a member of the Automotive
Journalist's Association of Canada (AJAC).
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