Types Of Electric Wiring In Automobiles & How To Trace Faults In Them

Types Of Electric Wiring In Automobiles

Automobile manufacturers use wires of different colors for the different circuits so that defective circuits could be easily located.

Hence, in supplying electricity to different units, different types of electric wires are used. If these wires are left hanging there is every likelihood of short-circuiting and even fire may break out.

To avoid all these in automobiles, all the wires are grouped together, cotton-braided, and dipped into the chassis or body. This is known as the wiring harness.

While crippling the wire harness, care should be taken to avoid fixing up the harness near the exhaust pipe of the fuel line.


To light any bulb or make any electric unit work, connecting one positive wire and one negative wire along a part is the normal method.

It is a practice commonly seen in house wiring. When it comes to automobile wiring, the process seems the same.

Two wires will be needed which are the positive and the negative wires and they are connected in two ways in the automobiles; such connection systems are listed below:

Types Of Electric Wiring In Automobiles: Car, Three-Dimensional, Vehicle, Shape
Types Of Electric Wiring In Automobiles


The negative terminal of a battery is earthed to the body or chassis which is made of metal. As we know, metal is a good conductor of electricity.

Only wire is taken from the unit via switch and the negative terminal of that unit is earthed, in that way; one complete of wire is saved.

Due to the saving of electric wire, the earth return system is used in almost all present-day vehicles.


In this system, two wires that are the positive wire and the negative wire are taken from the battery to every unit.

The system of wiring is used only in costly vehicles and is compulsory for vehicles that are used for carrying explosives, petrol or oil tanker, and military vehicles.

Types Of Electric Wiring In Automobiles: Car Engine Prius C Motor Car Automobile Mo
Types Of Electric Wiring In Automobiles


When it comes to automobile wiring, two types of wires are used and they are:

  1. THE COTTON BRAIDED WIRES: for the copper brand, rubber or plastic is molded on top of it, cotton braided and then varnished to give insulation. These wires being costly are not much used.
  2. THE P.V.C. WIRES: for the copper brand, the plastic is molded as its insulation. It is cheap and easier to manufacture, hence; it is used more commonly than cotton braided wires.


Wires used in automobiles are grades that are, thin or thick wires according to the electric load they have to carry. Manufacturers usually supply in the wiring diagram.

The size of wire used for each circuit such as 14/.010 which means that this particular wire consists of 14 wires each having a diameter of .010”.

While replacing new wires, always use the correct grade of wire. In the case you used a thinner wire than the required size, firstly it will not carry the expected load.

Secondly; light illumination intensity will be affected and thirdly, the wire is likely going to heat up and melt the insulation leading to electrical shocks because of the overloading in it. The last condition of the wire could lead to a fire outbreak in any car.

In the same way, if you use thicker wire than the required size, it will increase the resistance and increase the total cost of the wiring.

Based on frequently used sizes of wires used for automobile wiring, the following grades of wires are available for such use:

  1. Wires for the self-starter to switch – 6mm 35/.12 for 12 volts and 8mm 65/.12 for 24 volt
  2. Headlight and tail light circuit — 4mm 14/.12 for 12 volts  and  6mm 35/.12 for 24 volts
  3. Roof light, brake light, indicator light – 4mm 14/.12 for 12 volts
  4. Battery cable 61 wire 21 gauge
  5. High tension cable 19/.020

To make a wire connection, remove the wire insulation by ½ inch, solder the thimble on it and tighten the thimble with the help of a screw nut or bolt.

In the case of a thimble and solder is not available, twist the wires to make a ring, put a cup washer and tighten with the fastener. Note; under no case, wire connections should be kept loose.


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Philip Nduka

Philip is a graduate of Mechanical engineering and an NDT inspector with vast practical knowledge in other engineering fields, and software.

He loves to write and share information relating to engineering and technology fields, science and environmental issues, and Technical posts. His posts are based on personal ideas, researched knowledge, and discovery, from engineering, science & investment fields, etc.

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