How To Fit A New Coil

How To Fit A New Coil?

When a car’s coil becomes faulty, its performance becomes extremely poor. This consequently gives the driver a very tough time. Thus, to ease their problems, we will teach you how to fit a new coil in this article.

A coil can malfunction for a myriad of reasons. For instance, one of the reasons for a faulty coil is that its high-tension part may become faulty. You will have to perform an advanced resistance check using an ohmmeter to check this. Therefore, this article will cover several other possibilities, and we’ll teach you the right way to fit a new coil.  

What is a coil?

A coil or ignition coil is simply a small electrical transformer. They convert the low volt in car batteries and transform it into adequate high volt to get the engine running. There is a separate ignition coil for each spark plug.

Signs of a faulty Coil

If your car starts exhibiting the following symptoms frequently, then it means you need to get its coil checked

  • Car backfires frequently
  • Fuel economy worsens with significantly less mileage
  • The car’s engine starts misfiring.
  • Poor acceleration and engine jerking

Replacement cost

A new coil’s costs vary and are dependent on your car’s model. However, on average, the cost may lie anywhere from $75 to $300. If you opt to get the coil replaced by a car technician, they will charge an additional $50 to $100. Thus, the replacement cost can go up to a minimum of $200 if you’re getting it replaced by a mechanic. In addition, a dealership will charge you even more.

How to Fit a new coil

Learning how to fit a new coil is futile if you cannot inspect the problem areas and pain points in the coil. Firstly, check if the wiring is correct and whether the spark plugs are functioning or not. The spark plug’s lead must be tightly fitted. Then, inspect the contact breaker points and check if their gap is accurate and whether they can open and close correctly or not.

If you can still put your finger on the exact problem, the coil has either burned out or failed. You can use a test lamp to check for faults in the coil.

Tools you’ll need

  • Tool kit
  • New ignition coils
  • Ohmmeter

Safety Precautions

Before you start doing anything, there are certain safety precautions that you must take. For starters, make sure you are working with a cool engine. Secondly, use a memory keeper to mitigate electrical damage if your vehicle responds poorly to the disconnection of the battery cable.

Remove the old coil

Disconnecting and then removing the oil coil is the first step. Start by disconnecting your car battery’s negative terminal. Then, find and replace the ignition coil. Mark the cables and wires going in the cable and then disconnect them. Lastly, remove the plug’s clip that runs on the coil’s side.

Check the test lamp

To check the test lamp, you should start by looking for the low-tension positive terminal of the coil. This terminal will be traveling from the ignition switch in the coil. Now, plug the test lamp’s crocodile clip to an earth point and push the coil terminal from the test lamp’s other end. If the current travels to the coil, then the test lamp will illuminate. If it doesn’t, it means the problem lies deep inside the electrical circuit.

You need to check the ignition switch’s wiring and then the switch itself. Also, check the wiring connecting the battery and switch. Now, look for the coil’s low tension negative terminal. It is usually marked as CB. Without moving the crocodile clip, push the terminal along the test lamp. If the lamp illuminates, it indicates that the coil’s low-tension part is functional. However, if it doesn’t, then you will have to replace the coil.

 If the coil’s LT part is functional, its high-tension part might be problematic. To test this, you need to perform an ohmmeter test.

Checking the Ohmmeter.

 You can use an ohmmeter to perform an advanced resistance check on the coil. Firstly, switch off the ignition. Then, Disconnect both the terminal oil’s low-tension leads. Connect each of the two ohmmeter’s leads to the low-tension terminal coil.

Check the ohmmeter’s readings. Your car’s workshop manual will show the exact readings for your car. If the ohmmeter’s readings are not correct (either too high or too low), then it means that the windings are either brunt, broken, or without insulation.

Fitting a new coil

Finally, let’s jump right in and learn how to fit a new coil. Start by connecting the plugin to the ignition oil’s side. You can easily slide it in. once it’s done, you’ll hear a click. If you don’t, it means the connector hasn’t fitted properly, and the coil may not work. To insert the connector correctly, pull it off and check for debris. Now, try fitting it again but be careful and not fire it; otherwise, you may break it.

Insert all the ignition cables in the coil in their given order. In the case of a single cable, plug it directly into the cable port. After connecting each cable in their specified order, you will hear a pop sound signally it has been fitted properly. Before fitting the plugs, you can cover the ports with a little bit of dielectric grease to ensure a strong connection.

The final step involves reconnecting the battery. Refit the cable inside the battery’s negative terminal. Tighten the bolt using a socket or a wrench and place the positive cable on the terminal. Be wary

Open Coils

Another type of coil known as the open coil is used in cars such as Opels and Vauxhalls. An open coil is contained in a square outer casing. It’s important not to touch any open coil with a running engine; otherwise, you’ll get an electric shock.

Since an open coil and a regular ignition coil have similar circuits, you can easily replace an open coil and install a regular coil.


In a nutshell, the primary benefit of learning how to fit a new coil is that you’ll save tons of money that you would’ve otherwise spent on dealership stores or car technicians. Other handy skills that you should know and know how to fit a new coil include inspecting the ignition system, checking the starter circuit, and installing resonators and radiator sealers.