There we were, strapped in and ready to hit the dirt. A turn of the key yielded only silence at a time when we should have heard the throaty V-8 roar to life. A second attempt had the same results. Stripping the harnesses off, we climbed out of the truck and started nosing around under the hood. After a few minutes we found the cause of our electrical malfunction. The ignition wire for the starter was not properly secured and the push-on connector had loosened up, leading to a poor connection.
Electrics and autos have gone hand-in-hand for many decades and the infusion of electrical components into new 4WDs is increasing daily. Whether you may be adding a new accessory or simply having to troubleshoot or repair an electrical problem, some basic knowledge of electrical theory and practice can be handy.
We see it time and time again, where people have electrical troubles ranging from just a buzzing noise in the stereo to some connection failure that grossly affects the starting or running of the vehicle. Basic auto electrics don't have to be all that complicated and some careful attention up front when installing components and routing wiring can save you big headaches down the road.
Most vehicles we drive are equipped with, and operate from, a 12-volt battery. Along with the alternator, this source provides all the electrical energy needed on our vehicle. The battery is used for starting purposes and can supply electrical power when the engine is not running. Once the engine has been started, the alternator can be actuated by the voltage regulator to supply the electrical requirements of the vehicle, and recharge the battery as needed.
There are two basic properties we deal with when discussing electrical systems: voltage and current. Voltage (volts) is the electrical potential, and can be analogous to water pressure in a tank. The greater the voltage, the more energy we can typically supply. Thus, a fully charged battery or properly operating alternator will provide brighter lights than will a lesser electrical source. Current (amps) is a measure of electrical flow through a conductor and can be compared to water flow in a pipe. Increased flow capability means that greater energy is available at the far end of our wiring path. As an example, this becomes especially important when trying to get that last pound of winch pull when you're stuck in the mud.
An electrical circuit consists of a complete loop or path. That is to say that in an operating circuit, current flows from the positive side of the battery to the device being powered, and then back to the negative side of the battery. If this path is interrupted at any point, the circuit is broken and the device will not function.
Since the same current flows around the entire loop, both positive power wires and ground
This brings up two points concerning how electrical circuits are wired. First, note that a switch can be placed inline to engage or disconnect the device of interest. Such a switch is generally placed on the positive wire leading to the device, such that the downstream wiring is left unenergized when the switch is off.
As current flows through a wire it is subjected to a slight resistance in the wire. This resistance causes some voltage loss, or drop, as the current travels through it to the end where your electrical device resides. If you use too small a wire, the voltage drop across the wire will be significant and the voltage available at the device will be somewhat less than the full battery voltage. Performance of that device can suffer.
Wire size should be chosen based on the current draw of the device in question. The table below shows the American Wire Gauge (AWG) sizes recommended for various current load requirements. These sizes are valid for runs up to about 15 feet. For longer runs, it is best to upgrade to a larger size (lower gauge number) wire. If in doubt, always go with the larger wire to ensure you have plenty of current capacity, and minimize voltage drop over the length of the wire.