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electrical power cable calculator chart for amp current draw and length
vehicle audio system wiring diagram
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wire crimp terminal connectors
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automotive relay
vehicle circuit breaker
automotive electrical wiring essential tool kit
stripping the end of an electrical wire

This chart can be used to determine proper wire gauge. First, figure out the amperage of your electrical component. Next, measure the required length of your wire. Then just plug those numbers into this chart to determine the proper gauge.

This is a diagram of a high-end audio system. While it might not be typical of the wiring you will encounter in your street rod or race car, it does illustrate how a well laid-out wiring diagram should look. All of the components are clearly marked, as are the paths for power, ground, and accessory wiring and locations for all grounds and fuses.

If you are rewiring an early car or truck, make life easy on yourself and get a complete harness like this Painless Performance 18-circuit universal harness. The harness has virtually everything you need to wire the whole truck, including a preterminated fuse block and color-coded circuits for lights, gauges and dash, electric fuel pump, distributor and coil, electric fan, heat and A/C, wipers, and more. Painless Performance also has fuel injection wiring harnesses to swap a late model fuel injected engine into your vehicle. Available for GM TBI, TPI, LT1, and Vortec engines, plus Ford 5.0Ls, the harnesses have color-coded circuits and relays for fuel injectors, distributor, electric fuel pump, ECU, starter, and all necessary sensors.

If you don't need to do a complete harness but want to update your fuse block or panel, Painless Performance has universal fuse blocks like this 12-circuit fuse block. The blocks are pre-wired and pre-terminated--Painless Performance even installed the fuses, horn relay, and flashers for you. If you just want to increase the capacity of your electrical system to handle more accessories, you can get add-on fuse blocks from Painless Performance and Summit Racing.

You can never have enough solderless terminals around when you're doing a wiring job. Painless Performance has a nice 84-piece terminal set that should get you through a basic vehicle harness install. The set includes butt, spade, ring lug, and bullet terminals for 12-10, 16-14, and 16-18 gauge wire.

Speaking of wire, don't use cheap hardware or discount store wire in your electrical system. For a little more money, you can get high quality, automotive-rated wire. This Summit SAE Type GPT wire has a stranded copper core with a cover that is resistant to gasoline, acids, and grease. It's available in a variety of colors in 18- through 10-gauge sizes.

Switch panels are ideal for grouping electrical accessories in one convenient place for race cars and off-road vehicles where getting to electrical accessories quickly can be critical and where space can be at a premium. This Moroso switch panel has easy-to-use toggle switches to control five fused circuits; each circuit has front-mounted fuses and indicator lights. Remember to use relays in conjunction with your switches to help them handle the high current of aftermarket electrical accessories.

Relays help take the load off your switches by directing current to their assigned electrical accessory only when the switch is activated. This prevents the switch from overloading, especially with high-amperage accessories like big electric fans and off-road lighting.

A circuit breaker will switch off power to a protected accessory in an overload situation. When the overload has been corrected, the circuit breaker is reset. Circuit breakers like this Standard Motor Products 20 amp breaker come in manual reset and automatic reset versions, and in the same popular amperage ratings as fuses.

Did you lose all of your wiring tools? Well, relax--we have you covered with this Caspers Electronics wiring and connector maintenance kit. It includes the basics--double-d wire crimp tool for sealed and unsealed terminals, two rolls of high-temperature OEM wire harness tape, Weatherpack and Metripack removal tools, seam ripper for removing old tape on harness without damage, wire stripper for 24-12AWG wire, and a digital multimeter with batteries--to diagnose and repair most everything on your electrical system. You even get a handy carrying case.

The wire stripper in the Caspers' Electronics kit is good, but this Summit Racing wire stripper is even better. The spring-loaded tools will make quick work of your wires. Just insert the wire, squeeze the handle, and click--the wire is stripped and ready. The wire stripper also features an adjustable wire length guide that helps you make uniform strips, a built-in cutter, and a built-in crimping tool.

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Cars are filled with stuff that can make or break performance. The engine needs to be fed the proper amounts of air, fuel, and spark. The suspension and brakes must be in tip-top shape. The wheels and tires, transmission, cooling system, gauges—even the seats—must all function properly.

With all those things to worry about, many enthusiasts overlook the electrical wiring system. A lousy wiring job will keep your electrical accessories from operating at full potential—and that means subpar performance.

Many people are intimidated by the prospect of wiring a vehicle. But a proper wiring job doesn’t have to be a scary task—we’ve put together a few tips to help make the job a little bit smoother.

Round Up The Right Tools

The proper tools will make your wiring job a whole lot easier. Start with a quality set of wire strippers. Wire strippers generally include a group of holes to fit most wire gauges. This allows you to strip the insulation off your wires without accidentally cutting into the wire conductors.

A good wire crimper is necessary when you install solderless connectors. Most quality crimpers have two or three sections on the nose to fit various lug sizes. You can even get crimpers with wire cutting and wire stripping sections.

A soldering iron is a must for splicing wires or securing oversized connectors that cannot be crimped. You will need solder designed specifically for electronics and wiring . It has a midly activated rosin core flux to clean the wire as it is being heated, removing oxidation and light corrosion. That allows you to solder with less heat, making the connections stronger with less electrical resistance.

Here are some other items that should be in your electrical toolbox:

  • A wire brush for removing heavy corrosion, oil, or grease before soldering
  • A volt/ohm meter to measure voltage and resistance levels in your circuits
  • A test light to test for power within a circuit
  • Shrink tubing to insulate connections from outside elements. The tubing slides over the connector or solder joint and permanently shrinks when heated

Gauge Your Wiring Needs

A factory wiring harness includes the necessary wiring for standard electrical components like windshield wipers, horn, headlights, etc. However, when you add electrical or electronic components to your vehicle, like high-end audio or racing electronics, you need to choose the proper wire on your own. There are three factors to consider: size, material, and color.

Wire size is measured by gauge—the smaller the gauge number, the larger the wire. The gauge you need depends on the current draw of the accessory and the wire length between the accessory and the power source. In general, the larger the current draw, the larger gauge wire you need to properly power the accessory.

Wire Gauge to Wire Diameter Comparison Chart

Wire Gauge
(AWG)		Wire Diameter
(Inches)
4-00.460
3-00.409
2-00.364
00.329
10.289
60.162
80.128
100.101
120.081
140.064
160.050

One factor to consider with long lengths of wire is voltage drop. The longer the wire, the greater the voltage drop. You can offset voltage drop by increasing the size of the wire. As a rule of thumb, try to maintain a less than .5% voltage drop to assure maximum performance.

Wire material is usually aluminum or copper. For automotive purposes, we recommend stranded copper wire for the greatest flexibility and conductivity.

Wire color may not seem important at first glance, but it becomes crucial when you try to trace a faulty circuit down the road. To keep yourself from tearing your hair out, color-code your wire by accessory. It will help you keep track of which wire goes where during installation and troubleshooting.

Make the Connection

There are two main types of connectors: soldered and solderless. Soldered connectors are necessary with oversized wiring or if you’re splicing wires together. Solderess, or crimp, connectors can be used for most other wiring, and we’d recommend using them wherever possible.

Solderless connectors are the easiest to use and provide a good, strong connection. Usually, solderless connectors come with color-coded insulators, so you know which gauge wire they are designed for. Solderless connectors come in a variety of configurations:

Butt connectors are shaped like cylinders and are ideal for joining two wire ends together. A wire end is inserted into each end of the connector, which is crimped to complete the connection.

Spade connectors are ideal for components that are removed or serviced often. A male connector on one end of the wire fits into a female connector on the other end of the wire, completing the connection. To disconnect, just pull the connectors apart.

Ring connectors are used to secure wire to screw-type terminals; they are secured by the terminal screw.

When installing any type of connector—soldered or solderless—it is a good idea to use shrink tubing. Shrink tubing is relatively easy to install and provides added protection against electrical shorts and outside elements.

Choose the Right Components

There is more to wiring a vehicle than, well, wire. For example, you will need some sort of overload protection to protect your expensive electronics. The three basic types of overload protection are fuses, fusible links, and circuit breakers:

  • Fuses are designed to blow when the circuits they protect are fed more power than the fuses are rated for. Fuses are rated by amperage; popular sizes are 3, 4, 5, 6, 7.5, 10, 12.5, 15, 20, 25, and 30 amp. Always use a fuse rated slightly higher than the accessory. For example, if an electric fan is rated at 19.5 amps, use a 25 amp fuse.
  • Fusible links are another option. They are special wires made from an alloy with a lower melting point than regular copper wire. The link is spliced inline with an accessory’s power wire. In the event of an electrical overload the link will melt, preventing power from reaching the protected accessory.
  • A circuit breaker will switch off power to the protected accessory in an overload situation. When the overload has been corrected, the circuit breaker is reset. Circuit breakers come in manual reset and automatic reset versions, and in the same popular amperage ratings as fuses.

You should also install relays with your wiring if your electrical accessories require a bigger current draw than a standard power switch is rated to handle. And since most switches are designed to work with very limited currents, relays are required just about every time to wire a new aftermarket electrical accessory.

Relays are extremely useful for handling high-amperage electrical accessories like large electric fans, fuel pumps, and HID headlights. They are activated by an electric coil and controlled by a switch. When the relay is closed, no power goes to the accessory in question. When you flip the accessory switch, an electric coil in the relay opens, sending power to the accessory.

There are plenty of other products to make your wiring tasks easier, including switch panels, multi-circuit main and auxiliary fuse blocks, toggle, push-button, and remote-mount switches, and of course, wiring harnesses for everything from fog lights and gauges to complete vehicles.

Map Out a Plan

Before you begin your wiring project, map out a plan. Lay out the wiring or wiring harness so you know where each wire goes and that you have enough wire to complete the job. Locate the fuse box in an easy to reach location like your glove compartment or center console. Place the necessary relays, fusible link, or circuit breakers at connections between your power source and your electrical accessory.

If the wiring isn’t labeled already, label each wire or harness with the name of the components they route to. If the wiring or harness will be going through the firewall, use a grommet in the hole so the sheetmetal won’t cut through the wires. Don’t secure the connectors until the wiring is through the firewall.

Choose a spot on or near the firewall for the common ground point for the harness, and one point for a chassis ground on the negative side of the vehicle. This method gives you a single path to the negative side of the vehicle and provides a more effective ground. Use 10 gauge or bigger wire to connect the common ground to your chassis ground.

Take your time, stay organized, remain calm, and you’ll be a wiring wizard before you know it!

Keywords
automotive wiring, car electronics, car wiring, circuits, fuses, relays, wiring tips
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Author: David Fuller

David Fuller is OnAllCylinders' managing editor. During his 20-year career in the auto industry, he has covered a variety of races, shows, and industry events and has authored articles for multiple magazines. He has also partnered with mainstream and trade publications on a wide range of editorial projects. In 2012, he helped establish OnAllCylinders, where he enjoys covering all facets of hot rodding and racing.