HomeTips & GuidesWhat Gauge Are Car Wire Harnesses?

What Gauge Are Car Wire Harnesses?

What Gauge Are Car Wire Harnesses? If you own a car, you’re probably aware that there are a number of wires used in the car’s wiring harnesses.  These include the primary wire, battery wire, automotive speaker wire, and brake wire.

These automotive wires, each designed for specific purposes, make the right choice challenging. However, every wire has its own unique electrical properties with a certain gauge, making it ideal for certain applications.

Read the article below to help answer the question: what gauge are car wire harnesses?

Table of Contents

Car Wire Harnesses Gauge Understanding:

A wire gauge is the measure of a wire’s diameter. 

The gauge size determines the amount of current a wire is capable of safely handling. Also, it identifies the electrical resistance and weight of the wire. 

Normally, wires are labeled with the gauge number followed by the text ‘AWG’, which refers to the American Wire Gauge.

In car wire harnesses, the most common AWG sizes include 18, 16, 14, 12, 10, and 8 AWG. The smaller the AWG size, the bigger the wire.

Very big wires might measure with a number of zeroes. Therefore, a 000 AWG is bigger compared to the 00 AWG wire.  For automotive applications, the largest wire you’ll find is probably 00 AWG.

A 4 AWG wire can handle up to 70 amps, while a 20 AWG wire can only handle 5 amps. As the gauge size decreases, the number of amps it can handle increases.

The electrical resistance per unit length of a 7 AWG wire is 0.50 milliohm per foot, while that of a 10 AWG wire is 1 milliohm per foot.

Therefore, a decrease in AWG size results in a decrease in the resistance per unit length as well.

It’s important to keep in mind that as the AWG size decreases, the wire’s diameter increases, the ampacity increases, and the resistance decreases.

Wiring harness of different gauges

Wiring harness of different gauges

Factors That Determine Car Wire Harness Gauge

Below are the two main factors that determine the best AWG size cable for a car wire harness connection.

  • Amperage

Signal wires such as those from sensors to your computer don’t need to be big as the current (amperage) is rather low.

However, major power wire applications like electric motors (locks, windows, etc.), alternators, and other high-draw components require a bigger wire capable of supporting the load.

  • Distance:

Whenever you run a wire, there’s a particular amount of voltage drop. This is similar to a water hose, where the longer the hose, the lower the pressure at the outlet. 

Most manufacturers specify a bearable total voltage drop on positive and negative terminals around 0.5 volts for a 12-volt engine and 1.0 volts for a 24-volt engine.

If the voltage drops below this threshold, your electronics may not function as intended.

However, with electric circuits, you can battle voltage drop using larger AWG wires. 

So, what gauge are car wire harnesses?

This is the recommended gauge at 12 volts while maintaining a 3% or lower voltage drop at a certain amperage and length.

Whatever chart you use, ensure the chart’s voltage drop is noted. The table below uses a standard 3% voltage drop. 

If the voltage drop goes beyond 3%, then the efficiency of the components in the circuit significantly decreases and shortens the equipment’s lifespan.

Which Gauge Wire To Use Wire Length in Feet (From Battery to Starter)
0 – 44 – 77 – 1010 – 1313 – 1616 – 1919 – 22
Amperes (Ampacity of the Starter)0-2012121212101010
35-501010108884 or 6
50-651010884 or 64 or 64
65-8510884 or 6444
85-105884 or 64444
105-125884 or 64442
125-15084 or 644222
150-2004 or 644221/01/0

Common Applications of Standard Car Wire Harness Gauges

Different wire harnesses use different AWG sizes depending on the components you connect.

Car Wire Harness AWG SizeApplication
22 or 20 AWGSensors
18 AWG or smallerNon-sub-woofer speakers
16 AWGConveying current to your ignition coil and from the generator to your starter for vehicles with interior lights, tail lights, and parking lights.
12 – 14 AWGTransporting power from your battery to the high draw accessories like the main fuse block, windshield wiper, fuel pump, 12 V cigarette lighter, horn to relay, and headlights.
10 AWG and sometimes 8 AWGRun from the generator or alternator to anything. Also, it powers long circuit runs from the front-mounted battery to high-draw accessories found at the rear of the car (vehicles using trunk-mounted compressors or powerful amplifiers).
8 AWGFor low compression, small displacement motors. 
4 AWG and 6 AWGFor standard batteries and starters.
0 AWG and 1 AWGare Used to wire the starters of diesel and high-compression gas engines.
00 AWGUsed in large trucks for conveying current from multiple batteries.
Car Window Wipers

Caption: Car Window Wipers

How to calculate the exact car wire harness gauge to use

The chart above makes it easier to determine the size of wire you need to use. However, if you prefer to do the calculation yourself, you can use this formula:



  • 𝐀 – refers to the C.S area in m2.
  • 𝐈 – refers to the max current through the wires in amps. The amperage draw depends on the oil viscosity, engine size, temperature, and condition of the starter motor. A standard four-cylinder engine uses between 125 amps – 150 amps.
  • 𝐩 – this is the resistivity of the conductor. A standard PVC-coated copper cable normally used in cars measures a resistivity of around 1.7 X 10-8 Ωm. 
  • 𝐋 – the length of the wire in meters, which is the cable length from the starter to the battery in meters.
  • 𝐃 – this is the max allowable voltage drop in volts.

The formula above will help you get an m2 metric value.

Then, you’ll need to convert it to square millimeters: Area in m2 X 106= Area in mm2.

Now, you can use the table below to determine the equivalent value in the AWG system (in the range between 2/0 – 12).

AWG SizeMillimetersInches

Examples of car wire harness gauges using,

let’s begin with, a standard 12 V circuit running the power windows. 

Door Window Wire Harness Gauge

A standard fuse in the fuse panel is rated 25 amps, meaning the highest capacity of the circuit is 25 amps. This generally allows for a 10% – 15% variance in a draw. Therefore, the window motor only draws about 20 amps. 

Another instance is if you pinched the wire in your door and now have to replace it. The standard automotive primary wire is normally 18 AWG. 

However, this is ideal for signal wires but not high-current applications. Therefore, if you replace that part of the wire with an 18 AWG piece, it could potentially spark a fire.

It’s important to match the size of the original wiring, which is often a 12 AWG that services 25 amps for 10 ft – 12 ft. This is almost the correct length for your door window to the power source.

Audio Amplifier Wire Harness Gauge

If you plan to install an audio amplifier in your vehicle, the amplifier has 2 fuses, each using 30 amps. 

To determine the size of the wire, you’ll need to figure out the approximate length of the wire. Remember, the wire covers the distance from your battery to the amp installation point (all amps must be directly wired to the battery). 

For example, if the wire needs to be over 16 feet, using a 50 amp circuit, and has a 3% voltage drop, you’ll need to use a 4 AWG power wire. 

Auxiliary Light Wire Harness Gauge

For instance, with auxiliary lights, you probably have a 60-watt premium work light; divide that by the 12 V of power supplied to it, and you get an amperage draw of exactly 5 amps.

However, usually, you’ll have a pair of these lights, meaning you’ll be pulling around 10 amps for both lights. 

Although this doesn’t seem like a lot of power, it’s a constant flow. Also, it might be over a decent distance to get there; therefore, when it comes to an auxiliary light circuit, it’s best to aim for 16 AWG with a minimum of an 18 AWG wire in the circuit.

However, if it is a turn signal, tail light, or decorative light that doesn’t have a heavy wattage circuit, doesn’t pull too much power, and isn’t under a load as constant as an LED light bar or auxiliary light, you can opt for the 20 AWG or 18 AWG depending on the distance for the circuit.

LED Powered Brake Light

Caption: LED Powered Brake Light


Choosing the best wiring for automotive applications is an important part of ensuring your car’s electrical systems are operating properly. In case of any further queries, feel free to reach out to Cloom Tech.

Hi I am Christa, sales manager of Cloom.

I have extensive expertise and experience in wiring harnesses and I believe I can help you.

And we have a very professional technical team who can clearly understand the customer’s needs and give professional suggestions and solutions after receiving the drawings.

If you also have wiring harness needs, please send me the drawing so that we can give you our quote and start our business.

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