Total Performance King- Hot Rod Girl: Part IX

Wires And Terminals
Wires and terminals come in a variety of sizes for a reason. Larger-diameter wires have lower gauge numbers; smaller-diameter wires carry higher numbers (in other words, a 10-gauge wire is thicker than a 12-gauge wire). Higher-amperage circuits require larger-diameter wire and terminals with higher ratings. The same is true if you are running an extra long circuit or bundling multiple circuit wires together in a loom. Just like switches, these parts need to be sized to carry the appropriate amperage and need to be able to ventilate to prevent heat buildup. Contrary to some people's beliefs, soldered connections are not a necessity; a good crimp joint is fine. In fact, if you're not careful, it's very possible to overheat a solder joint, causing a brittle connection that could break due to movement and vibration. As a rule, the OEMs use crimp joints for nearly everything, including many main battery connections, and if billions of dollars of R&D justify crimped joints, then they're good enough for me.

Every single piece in a circuit has that circuit's total amperage running through it and needs to be sized accordingly. The things to consider when selecting a wire size and insulation are the current the wire will carry, the total length of the wire, and how much voltage loss is acceptable. (There is always some loss-the longer the wire, or the smaller the wire, the more the loss.) As a general rule, sensitive circuits and headlights can tolerate 3-percent loss, and most everything else can tolerate 10-percent loss. Headlights are sensitive because the light output varies as the square of the voltage or more. So if you want the best light output you can get, use a heavier gauge wire and use a relay. Also, EFI, ECM, and stereo systems have high peak-current requirements that demand a larger wire size.

Breakers And Fuses
A circuit breaker is a safety device that's designed to protect an electrical apparatus from damage caused by overload or short circuit. You're probably most familiar with circuit breakers from the electrical panel in your home. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.

A fuse performs the same task as a breaker but is much smaller and must be replaced after it trips. 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 break the circuit. A blown fuse must be replaced with a fuse of the same amperage. If you've got a fuse that keeps blowing, find the problem. Installing a higher-amp fuse and hoping for the best can cause significant damage or fire. Nearly all aftermarket harnesses use modern spade fuses instead of the old glass tube style.

Fusible links are used in some harnesses, as well. Much like a fuse, fusible links are short lengths of wire designed to melt at a certain current rating. They are commonly used instead of an inline fuse in main power leads to prevent current spikes from damaging the fuse block or harness.