The mundane-sounding components of wires, fuses and connectors are found in every electrical device, and especially in cars. Many of the features we have come to expect in our cars are possible because of these elements, and their reliability has improved immensely in the last couple of years.

Along with increased reliability, the complexity of car wiring systems has increased dramatically. Cars now have literally thousands of circuits.

 

Wires
A car's wiring has to distribute power from the battery to devices located all over the car. It also has to transmit data on a data bus, as well as a variety of digital and analog signals from switches and sensors.

This means that there are many different types of wires in your car. Some wires that transmit signals from switches or sensors carry almost no current. Those that provide power to large electric motors carry lots of current.

If too much current goes through a wire, it can overheat and melt. The amount of current that a wire can handle depends on its length, composition, size and how it is bundled. Let's take a quick look at how each of these properties affects the wire's current-carrying capacity:

• Length - Each type of wire has a certain amount of resistance per foot -- the longer the wire, the larger the resistance. If the resistance is too high, a lot of the power that flows down the wire will be wasted; the energy lost as heat builds up in the wire. Ultimately, heat build-up limits the current-carrying capacity of the wire, as the temperature must not get hot enough to melt the insulation.
• Composition - Automotive wire is usually composed of fine copper strands. Generally, the finer the strands, the lower the resistance and the more current the wire can carry. The type of copper used has an effect on the resistance of the wire, too.
• Wire gauge - The wire gauge, or size of the wire, also determines how much resistance the wire has. The larger the wire, the less resistance. The smaller the gauge, the larger the wire -- so a 16-gauge wire is bigger than a 24-gauge wire. Wire gauges go all the way down to zero, which is also called 1/0 (one aught). Even bigger than 1/0 is 00 (2/0, or two aught), and so on. The diameter of a 4/0 (four aught) wire is almost half an Bundling - The way a wire is bundled affects how well it can dissipate heat. If the wire is in a bundle with 50 other wires, it can carry a lot less current than if it were the only wire in the bundle.

Fuses
The main job of the fuse is to protect the wiring. Fuses should be sized and located to protect the wire they are connected to. If a device like your car radio suddenly draws enough current to blow the fuse, the radio is probably already toast. The fuse is there to protect the wire, which would be much harder to replace than the radio.

Most cars have two fuse panels. The one in the engine compartment holds the fuses for devices like the cooling fans, the anti-lock brake pump and the engine control unit -- all of which are located in the engine compartment. Another fuse panel, usually located in the dashboard near the driver's knees, holds fuses for the devices and switches located in the passenger compartment.

The heat build-up in the wire depends on the resistance and the amount of current flowing through the wire. Fuses are really just a special type of wire in a self-contained connector. Most automotive fuses today have two blade connectors and a plastic housing that contains the conductor. There are also some fuses that are in the wiring of the car, called fusible links.

The conductor inside the fuse is made of a metal similar to solder. It has a lower melting point than the wire itself. The size of the conductor is calibrated very carefully so that when the rated current is reached, enough heat is generated to melt the conductor and so break the circuit.

When a fuse is blown, it must be replaced before the circuit will work. A blown fuse must be replaced with a fuse of the same amperage.

 

Connectors
Connectors are critical to today's cars. Without them, it would be nearly impossible to build or service a car. Whenever a bundle of wires passes through or attaches to a component of the car that might have to be removed, there must be a connector there to allow for that removal. A single connector can have more than 100 wires.

In the past, unreliable connectors have been the source of many electrical problems. Connectors have to be waterproof (modern connectors have several seals to keep out moisture), corrosion proof and provide good electrical contact for the life of the vehicle.