Which wire from the ignition coil goes to the distributor?

The thick, high-tension wire from the coil’s center tower goes to the center of the distributor cap, and the small negative (-) primary wire from the coil typically connects to the distributor’s points or ignition module. In most negative-ground vehicles, the coil’s positive (+) terminal gets switched 12V from the ignition switch (often through a ballast resistor on points systems), while the negative (-) terminal is the one that the distributor controls to switch the coil. Below is a detailed breakdown of how to identify and connect these wires correctly across common ignition setups.

Understanding ignition coil connections

Classic distributor-equipped engines use two distinct circuits at the coil: a low-voltage primary circuit and a high-voltage secondary circuit. Each has a specific destination and purpose, and mixing them up will prevent the engine from starting or can damage components.

• Coil center tower (high-voltage/secondary output): Connects via a thick, heavily insulated lead to the center post of the distributor cap.
• Coil “-” (negative) primary terminal: Connects to the distributor’s points or electronic ignition module, which switches the coil on and off to create spark.
• Coil “+” (positive) primary terminal: Receives switched 12V from the ignition switch; on points systems this is usually routed through a ballast resistor or resistance wire.
• Grounding: The coil body is typically grounded through its bracket; do not add separate grounds to the primary terminals unless specified by the vehicle’s wiring diagram.
• Polarity note: On older positive-ground vehicles, terminal roles can be reversed or labeled differently (e.g., SW/CB). See “Polarity notes and exceptions” below.

If these connections are made correctly, the coil will step up voltage and the distributor will route spark to each cylinder in order. Incorrect wiring typically results in weak/no spark or backfiring.

Variations by ignition system

Points-style (contact breaker) systems

These older systems use mechanical points inside the distributor to switch the coil. Correct wiring and ballast use are critical for reliable spark and point life.

1. Run a thick high-tension lead from the coil’s center tower to the distributor cap’s center terminal.
2. Connect the coil “-” terminal to the insulated post on the side of the distributor (this lead goes to the points/condensor inside).
3. Feed the coil “+” terminal with switched 12V from the ignition switch through a ballast resistor or resistance wire (many systems also supply full 12V during cranking via a starter bypass lead).
4. Ensure the distributor is well grounded via its mounting to the engine block.

With this setup, the distributor points interrupt current on the negative side of the coil, collapsing the field and generating spark that is routed via the distributor cap and rotor.

Electronic ignition with an external coil (e.g., Ford Duraspark, Chrysler ECU, GM HEI remote-coil)

These systems replace points with a module that switches the coil. The “coil wire” to the distributor cap is still the high-tension lead, but the primary wiring follows the module’s diagram.

• Coil center tower to distributor cap center via the thick high-tension lead.
• Coil “+” terminal to switched 12V (some systems still use a ballast; others require full 12V—follow the factory diagram).
• Coil “-” terminal to the ignition control module’s coil negative output (the module receives triggers from the distributor pickup).
• Module and pickup wires must be connected exactly per the manufacturer’s color code and polarity.

Here, the module controls dwell and switching, improving reliability over points. Always verify whether your module requires a ballast resistor to avoid overheating the coil.

Coil-on-plug or distributorless systems (for context)

Modern engines without a traditional distributor do not use a single center high-tension coil wire. Instead, they use individual coils or coil packs controlled by the ECU. If your engine has a conventional distributor cap and rotor, your configuration is one of the first two types above.

How to identify the correct wire on your car

When the harness isn’t labeled, these practical clues will help you map the coil-to-distributor connections correctly and avoid polarity mistakes.

• Look for the coil’s center high-voltage tower: it takes the thick “coil wire” to the center of the distributor cap.
• Find the “+” and “-” markings on the coil primary posts (sometimes “BAT” for + and “DIST” for – on older coils).
• Trace the small wire exiting the distributor body: it typically goes to the coil “-” or to the ignition module that then connects to coil “-”.
• Identify the ignition feed: a switched 12V source (often via ballast) goes to coil “+”. Colors vary by make/model; consult a wiring diagram if uncertain.
• Confirm with a multimeter: with key ON, coil “+” should have battery voltage (or ballast-reduced voltage), while coil “-” will be switched to ground during cranking/running.

Using these indicators will ensure you connect the right leads without relying solely on color codes, which can differ across manufacturers and years.

Polarity notes and exceptions

Most vehicles since the late 1960s are negative-ground, meaning the coil “-” terminal is the side switched by the distributor or module. On some older positive-ground vehicles (common in vintage British cars), coil terminals may be labeled “SW” (to the ignition switch) and “CB” (to the contact breaker/distributor). In those systems, the distributor may connect to the coil’s “+” or “CB” depending on grounding scheme. Always verify vehicle ground polarity and follow factory labeling: SW to ignition feed, CB to distributor contact breaker.

Safety and basic testing

Ignition systems generate very high voltages. Missteps can cause shocks or damage components. If you need to test for spark, do so carefully.

• Use insulated pliers and a proper spark tester; avoid holding bare terminals.
• Keep fuel vapors and open flames away while cranking.
• Do not crank the engine with the coil secondary lead disconnected and dangling—always provide a safe spark gap.
• If components run hot or the coil hums loudly with key ON and engine off, recheck ballast requirements and wiring.

Observing these precautions will help you diagnose and confirm correct wiring without risking injury or component failure.

Summary

The coil’s center high-tension tower connects to the center of the distributor cap, and the coil’s negative (-) primary terminal typically connects to the distributor’s points or ignition module, while the positive (+) terminal receives switched 12V. Ensure correct polarity, ballast use (on points systems), and follow any module-specific diagrams to guarantee a strong, reliable spark.

Does power go from coil to distributor?

When you turn the key in the ignition switch, it sends an electrical signal to the ignition coil, which then generates a high-voltage pulse. This pulse is sent to the spark plugs via the distributor or ignition module, which creates a spark that ignites the fuel-air mixture in the cylinders.

What wires go to the ignition coil?

The wires going to an ignition coil include a power supply (battery voltage), a ground wire, and a control or trigger wire from the engine’s computer (PCM) or an older mechanical system like a distributor. The number and type of wires depend on the ignition system, with common setups including three-wire coil-on-plug (COP) systems using a power supply, ground, and a trigger signal, and four-wire systems adding a diagnostic feedback circuit. For older distributor-based systems, you’ll find positive and negative wires to the coil from the battery/ignition switch and a control wire from the distributor’s points or electronic module.
 
This video explains the basic concept of an ignition coil and its role in generating a spark: 58sCarParts.comYouTube · May 31, 2023
Three-Wire Ignition Coils
These are common in modern coil-on-plug systems and have three main connections: 

1. Battery Voltage Power Supply: Provides constant power from the battery when the ignition is on. 
2. Ground: A full-time connection to the vehicle’s chassis. 
3. Control Circuit (Trigger): A signal from the Powertrain Control Module (PCM) that tells an internal transistor when to fire the coil. 

Four-Wire Ignition Coils
Similar to three-wire systems, four-wire configurations add an extra circuit for diagnostic purposes: 

1. Battery Voltage Power Supply: Same as above.
2. Ground: A chassis ground connection.
3. Control Circuit (Trigger): The PCM’s signal to fire the coil.
4. Diagnostic Feedback (IGF) Circuit: A signal that provides feedback to the PCM about the coil’s operational status.

This video demonstrates how to connect an ignition coil in a distributor-based system: 1mLet’s Build a Willys JeepYouTube · Jul 23, 2022
Older Distributor-Based Ignition Coils
In systems using a distributor and external coil, the wiring is simpler: 

1. Positive Wire: Connects to the battery or ignition switch power. 
2. Negative Wire: Connects to the points or electronic control module, which interrupts the circuit to “fire” the coil. 
3. High Tension Wire: A thick, insulated wire that runs from the coil’s center to the distributor cap or directly to a coil-on-plug assembly. 

Which side of the coil goes to the distributor?

The distributor wire connects to the negative (-) side of the ignition coil on a typical 12-volt negative-ground vehicle system. The positive (+) side of the coil receives power from the ignition switch, usually through a ballast resistor, while the distributor wire completes the circuit by connecting to the coil’s negative terminal, which is also connected to the breaker points or electronic ignition within the distributor.
 
Here’s a breakdown of the wiring for a common 12-volt system:

1. Distributor Wire to Coil: Opens in new tabThe wire from the distributor (connected to the points or electronic ignition) goes to the negative (-) terminal of the ignition coil. 
2. Coil Positive Terminal: Opens in new tabPower from the ignition switch (often with a ballast resistor for voltage reduction while running) connects to the positive (+) terminal of the coil. 
3. Circuit Completion: Opens in new tabThis setup allows the ignition switch to provide power to the coil’s positive terminal. When the distributor’s points open, they interrupt the ground path at the coil’s negative terminal, creating a surge of high voltage in the coil that is then sent to the spark plugs. 

Why This Wiring is Necessary:

• Voltage Spike: Opens in new tabThe circuit from the distributor’s ground connection to the coil’s negative terminal is what creates the high-voltage spark. 
• Correct Polarity: Opens in new tabConnecting the distributor to the negative side ensures the correct polarity and allows for proper function. Incorrect wiring can reduce the coil’s lifespan and spark efficiency. 

Key Takeaway:
On a standard 12-volt system, the distributor’s internal mechanism controls the timing of the spark by making and breaking the connection to the coil’s negative terminal.

What is the wire from the coil to the distributor called?

The single low-voltage wire from the coil’s negative terminal connects to the points inside the distributor, which then grounds the coil to complete the circuit and generate a spark. The exact color of this wire can vary, but it’s the low-voltage lead, not the thick high-tension (spark plug) wire that goes into the distributor cap’s center. Always verify the connections with a wiring diagram specific to your vehicle’s make and model.
 
Here’s a breakdown of the connection:

1. Low-Voltage Wire: There’s one specific wire that carries the signal from the coil to the distributor’s internal components, like the points. 
2. Negative Terminal: This wire connects to the negative (–) terminal on the ignition coil. 
3. Distributor Points: The other end of the wire attaches to the points mechanism inside the distributor. 
4. Grounding: When the points are closed, they provide a ground path for the coil, allowing the electrical current to flow and create a spark. 

Why this connection is crucial:

• Circuit Completion: Opens in new tabThis connection completes the low-voltage circuit. When the points open, they break the circuit, which causes the ignition coil to collapse its magnetic field and generate the high-voltage pulse. 
• Engine Timing: Opens in new tabThe distributor, with the help of the points, controls when this low-voltage connection is broken, thus timing the ignition to fire the correct cylinder. 

Key things to remember:

• Low-Voltage vs. High-Voltage: Opens in new tabDon’t confuse this with the thick, high-tension (HT) wire that goes from the center of the coil to the center of the distributor cap. That wire carries the high voltage to the rotor. 
• Vehicle Specifics: Opens in new tabAlways consult a wiring diagram for your specific vehicle to identify the correct wire and connection points. 
• Check for Corrosion: Opens in new tabEnsure all connections are clean and secure to prevent issues with your engine’s performance.