How to Wire Glow Plugs to a Switch? All You Need To Know

You can’t drive a car without starting it. Glow plugs come in handy. To start your car, it must reach a certain temperature.

A glow plug works by warming up the fuel and air to improve combustion. But before the ignition, the glow plug must be wired.

So, the question is how to wire glow plugs to a switch?

We will need a long cable to connect the battery with one of its large posts. Need to connect the other end of the cable with the glow plug. Now another heated wire should be connected to the small post of the battery. Bring the wire from other small post to the cable and connect it with the switch.

This was a glimpse of how to do it. To do it properly you will need further information which this article will provide.

Hope you will stick around.

How To Wire Glow Plug To a Switch

Glow plugs may appear inconsequential, but they are an essential component of every vehicle’s diesel system, and they serve a variety of critical functions.

Not just during the initial ignition, but also throughout the entire cycle, which is mostly overlooked because it occurs in the background.

To wire a glow plug to a switch consists of a few steps.

  • First of all, obtain a long cable to connect the battery to one of the large posts.
  • Connect the glow plugs to the opposite end of the cable.
  • After that, connect a heated wire to one of the small posts.
  • Bring another wire from the other small post all the way into the cab. And connect it to the switch.

What Exactly is a Glow Plug?

A glow plug is used in almost every diesel car. But you might need to know how a glow plug works? A glow plug in a diesel engine heats the fuel and air entering the engine to improve combustion efficiency.

Fuel combustion starts your engine, allowing you to drive. It is located either in the pre-chamber (for pre-chambered engines). Or the combustion chamber (for combustion chamber engines) of each cylinder.

Why Glow Plugs are Used?

Diesel engines require glow plugs to start. Glow plugs heat the combustion chamber air to the proper temperature to help it ignite.

Factors Affecting Choosing Glow Plugs

Glow plugs are classified into three different types, hot, medium, and cold. This classification is based on their temperature. The sort of glow plugs you require will be determined by a few different variables.


Your car’s ignition point is determined by the nitro percentage present in the fuel you use. Well, what is a nitro percentage in fuel?  It’s the amount of nitromethane available in the fuel.

Power and heat are produced by nitromethane. With a higher Nitro content, the cooler your glow plug should be. The standard engine requires a standard glow plug. But when it comes to a turbo engine it might require specialist plugs.

Engine Size

The fact that larger engines have more mass and hold more heat than smaller engines. Meaning that smaller engines require hotter glow plugs to function properly.


Hot glow plugs promote better acceleration and idling. Making them an excellent choice for engines that are slow while accelerating. Colder plugs provide greater power, which is good for engines that run at a high temperature.

How Many Glow Plugs Do You Need?

The number of glow plugs depends on the number of engine cylinders your vehicle has. One glow plug is required for each engine cylinder. Most of the cars use 4 or 6 cylinder engines which means these cars will require 4 or 6 glow plugs.

You may buy the best glow plugs from the following recommended products:

Should Entire Set of Glow Plugs Be Changed?

Always replace the full set of glow plugs when replacing them. Although not all of the plugs are problematic, only one or two of them are faulty, and the rest are in good working order.

Here you might have a question: Is it wise to change only the faulty plug? The answer is “No”.

They will shortly begin to be phased out one by one. Which means they will be out of service for quite some time. Because the replacement of the plugs is not particularly expensive. It is also advised that all of them be changed.

When Should You Change Your Glow Plug?

We often ignore glow plugs until they malfunction. To effectively maintain a diesel car, glow plugs must be changed. If you see a malfunctioning glow plug, replace the whole set immediately. Delay in changing glow plugs causes further damage.

In the case of a glow plug failure, your vehicle’s combustion chamber will be left cold. On hot days, a successful start-up may take multiple attempts. If your glow plugs are damaged or malfunctioning, your engine won’t start in the cold.

Here are several indicators that it’s time to replace your glow plugs.

Hard Starting

This is the most common sign of bad glow plugs. If you are in a cold climate and do not have a working glow plug, you may suffer. A faulty glow plug may prevent your automobile from starting. In this case, check the fuel, battery, and glow plugs.

Misfiring in Engine

A misfiring engine is usually one of the first indicators of glow plug difficulties. The engine will misfire if the glow plugs fail to produce the necessary heat for diesel combustion. So, when your engine misfires do check the glow plugs.

Rough Idling

In the event of a glow plug failure or damage, the engine will be difficult to start, idle rough, and emit white smoke for many minutes. Check the fuel injection timing if all glow plugs are burnt.

Decreased Fuel Efficiency

In some cases, diesel is treated with additives to lower its freezing point. Which provides  Less energy and less efficiency.

If the engine cannot achieve the proper temperature owing to malfunctioning glow plugs, it will suffer. And have to work harder to satisfy the needs of the road. The vehicle’s fuel economy will suffer.

White Smoke

White smoke can be caused by damaged glow plugs or a malfunctioning glow plug control module. White smoke indicates insufficient heat to burn the fuel. Unburned fuel particles exit the exhaust as smoke, smelling like rich fuel.

That’s all we had to say.


What is a glow plug module?

The glow plug control module uses data from the Engine Control Unit (ECU). This is to determine the glow plug timing and current requirements.

Is there a fuse for glow plugs?

A replacement fuse is not provided by the manufacturer. That is on the high current side of the glow plug system.

What does a glow plug harness do?

The Diesel Glow Plug Harness protects your car from oil leaks, hard starts, and no starts. This straight replacement harness gives power to the vehicle’s glow plugs and is built of durable materials.


If you are still reading, thank you very much. Hope you found the answer to how to wire glow plugs to a switch? If you are still facing some problems figuring it out please visit a service center for the solution.

Thank you and Good Luck!

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