HomeTips & GuidesWiring Coil to Distributor: Importance of This Wiring and the Wiring Steps

Wiring Coil to Distributor: Importance of This Wiring and the Wiring Steps

Here is a guide about wiring coils to distributors.

Modern vehicles don’t run using distributors, but you can find them in classic cars built in the 80s and 90s. 

This ignition system is crucial to the smooth running of a gasoline engine, and two critical components in the system are the ignition coil and distributor.

Some distributors, such as HEI systems, have the coil in the distributor cap. 

But most have the device externally mounted, meaning you need a high-voltage cable for wiring the coil to the distributor.

 Here’s how to go about this wiring process.

Table of Contents

Understanding the Distributor Ignition System

Before going into the wiring process, let’s step back and understand the ignition system. This system has three primary components.

Ignition Coil

An ignition coil is functionally a step-up transformer because it converts the low 12V battery voltage in the primary winding into a high voltage reaching 12-25kV in the secondary winding. Coils in large engines can take up to 40kV.

The internal structure of an ignition coil

The internal structure of an ignition coil

This high voltage is necessary to create a spark on the spark plug gap inside the combustion chamber to ignite the fuel-air mixture.

Sending low voltages to the spark plug can fail to create a spark, leading to inefficient combustion. 

But the higher the voltage, the hotter the spark and the longer it will last, ensuring complete burning.


Modern vehicles have Coil-on-Plug systems with electronic control and timing, eliminating the need for a distributor.

 These systems give more precise ignition timing, especially at high speeds.

But old engines rely on distributors, which have two functions.

 The first is to direct the high voltage from the ignition coil to terminals mounted on its cap. 

These terminals match the firing order in the cylinders.

The distributor and red distributor cap in a classic car engine

The distributor and red distributor cap in a classic car engine

The second function is to control timing. Distributors have a rotating arm or rotor that spins inside the cap to connect to the spark plug wires via the terminals, and the spinning speed controls firing timing.

This rotor should make a full rotation between the spark firing for each cylinder, meaning it spins at half the crankshaft’s RPM or the same RPM as the camshaft. The crankshaft and camshaft rotation speeds are topics for another day.

Spark Plugs

Spark plug wires exit the distributor via its cap, transmitting the high voltage charge via a thick (low wire gauge), well-insulated cable.

The distributor and red distributor cap in a classic car engine

A graphic image showing a distributor ignition system (note the firing order of the spark plugs and how it matches the terminals in the distributor cap)

Once the charge gets to the plugs, they emit a bolt of electricity across a tiny gap right after the fuel-air mixture flows into the cylinder. 

This bolt ignites the mix, setting the pistons in motion to keep the engine running non-stop.

Importance of Wiring Coil to Distributor Properly

This wiring is critical to running a gasoline engine due to these benefits.

Improves Fuel Efficiency

The high voltage line ensures power gets to the distributor at the required quantity for distribution to the spark plugs. 

This high-voltage charge delivery directly impacts fuel economy, ensuring cylinders burn the fuel completely to deliver maximum power.

A detailed view of a distributor ignition system with breaker points

A detailed view of a distributor ignition system with breaker points

Busted wires or other issues along the line can leak some of the power, cutting the amount that gets to the distributor, thereby affecting fuel economy.

Ensures Proper Ignition Timing

Proper wiring ensures the coil and distributor work in perfect harmony, resulting in precise timing when sparking. 

Precision timing makes the engine run smoothly while delivering maximum power to the wheels.

Enhances Engine Performance

Improper wiring can affect spark timing, resulting in reduced engine power output, poor acceleration, and even engine knocking in the worst-case scenario. But correct wiring can prevent these issues.

Maximizes Engine Lifespan

As stated earlier, incorrect wiring can lead to knocking, which can cause premature wear on specific engine components, such as valves and pistons. It can also lead to overheating and stress, resulting in further damage.

Ensure Vehicle Reliability

Correct wiring of the coil to the distributor ensures precise and consistent sparking timing, minimizing the risk of misfiring, stalling, knocking, and other ignition issues that can break down your vehicle on the road.

Reduces Emissions

Proper wiring leads to efficient combustion, meaning all the fuel sprayed into the cylinder burns. Therefore, your vehicle’s tailpipe will not emit carbon monoxide or unburnt hydrocarbons. The exhaust will only have water vapor and carbon dioxide.

Wiring Coil to Distributor: Steps To Follow

This wiring can vary depending on the vehicle, but here’s a general guide to handle the process. You will need these items before getting started.

  • Screwdriver
  • Wrench
  • Vehicle wiring diagram
  • Safety gear

Step 1: Disconnect the Battery

Before touching any ignition circuit in the vehicle, disconnect the power supply. Use a wrench to loosen the negative battery terminal, then remove it from the post.

Step 2: Wiring Coil to Distributor: Find the Ignition Coil and Distributor

Locate the coil and distributor in the engine bay. The former is usually cylindrical, but some have rectangular shapes. 

On the other hand, distributors are larger cylinders than the coil size, with a cap and wires protruding out of the cap.

Wiring Coil to Distributor: A rectangular-shaped ignition coil

A rectangular-shaped ignition coil

Step 3: Wiring Coil to Distributor: Determine the Distributor Ignition System Type

These distributor ignition systems come in two types. The old points type features a condenser and a set of points, and wiring involves linking the coil to these two parts.

Electronic ignition distributors are the second type, and they use electronic components instead of a condenser and point to handle the distribution and timing.

Check the vehicle’s wiring diagram to determine its distribution configuration, including the wire colors and their respective connections.

Wiring Coil to Distributor: A distributor ignition system with breaker points

A distributor ignition system with breaker points

Step 4: Wiring Coil to Distributor: Wiring the Coil to the Distributor

Wire the high-tension wire to the center terminal on the distributor cap relative to the spark plug wires. Next, connect the positive ignition coil terminal to the distributor’s positive pin. But this might not be necessary in some units.

Ignition coils also have negative ground terminals for connecting to the vehicle’s ground point or the negative terminal on the distributor. This link allows current to flow by creating a low or zero potential point.

Electronic distribution systems can have an ignition module between the coil and the distributor.

Wiring Coil to Distributor: An electronic ignition distributor

An electronic ignition distributor

Step 5: Wiring Coil to Distributor: Reconnect the Battery

Hook the negative battery terminal back on the lug and fasten its nut using a wrench.

Step 6: Wiring Coil to Distributor: Test the Ignition System

Here’s the moment of truth. Start the engine to check if it runs smoothly. Do a driving test, as well. This test will show you the acceleration performance.

Wrap Up

The wiring between an ignition coil and a distributor creates the first link of sending high voltage charge to the spark plugs. 

So, this section is critical because it ensures precise timing, improves engine performance, and lowers fuel consumption.

Ignition systems have other components, and we recommend reading this ignition switch wiring article to get a holistic view of the ignition system wiring process.

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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