Ford Falcon XK Ignition System Troubleshooting and Maintenance Guide

The ignition system used in the Ford Falcon XK consists of two primary electrical circuits that work together to produce the spark required to ignite the fuel mixture in the engine cylinders.

These circuits include:

Primary (Low Voltage) Circuit

Battery
Ignition switch
Primary circuit resistance wire
Primary windings of the ignition coil
Breaker points
Condenser

Secondary (High Voltage) Circuit

Secondary windings of the ignition coil
Distributor rotor
Distributor cap
High tension ignition wires
Spark plugs

When the breaker points are closed, current flows from the battery through the ignition switch to the primary windings of the ignition coil. The current then flows to ground through the closed breaker points.

When the breaker points open, the magnetic field inside the coil collapses rapidly, producing a high voltage surge in the secondary windings. This high voltage travels through the coil high-tension lead to the distributor cap, where the rotor distributes it to the correct spark plug.

This process repeats for every power stroke of the engine.

Ignition System Trouble Diagnosis

Ignition problems can occur in either the primary or secondary circuits, or may result from incorrect ignition timing.

A complete ignition system check should include inspection of the following components:

Battery and battery cables
Ignition coil
Distributor assembly
Primary wiring
Secondary ignition wires
Spark plugs

Quick diagnostic tests can help determine which component is faulty before disassembly.

Preliminary Ignition System Checks

Before performing detailed tests, inspect the ignition system for common problems.

Check for:

Corrosion or dirt on battery terminals
Loose battery cable connections
Poor electrical ground connections
Dirty or damaged distributor components
Loose or corroded wiring connections

Clean battery terminals using a baking soda solution if corrosion is present. Ensure all electrical connections between the battery, engine, and relay are secure.

Primary Circuit Faults

Loss of energy or malfunction in the ignition primary circuit may be caused by:

Defective primary wiring
Burned or incorrectly adjusted breaker points
Defective ignition coil
Faulty primary resistance wire
Defective condenser

These faults often result in weak spark or difficult engine starting.

Primary Circuit Testing

A complete primary circuit test involves checking the electrical path from the battery to the ignition coil and through the distributor to ground.

Excessive voltage drop in this circuit can reduce ignition coil output and cause:

Hard starting
Misfiring
Poor engine performance

Battery to Coil Test

To perform the battery-to-coil test:

Turn the ignition switch on with accessories and lights switched off.
Connect the positive lead of a voltmeter to the battery positive terminal.
Connect the negative lead to the battery terminal of the ignition coil.

If the voltmeter reading is 6.9 volts or less, the primary circuit from the battery to the coil is satisfactory.

If the reading exceeds 6.9 volts, possible causes include:

Poor electrical connections between the battery and coil
Defective ignition switch
Faulty resistance wire
Faulty relay-to-ignition switch wiring

Ignition Switch Test

To test the ignition switch circuit:

Leave the jumper wire connected and keep the voltmeter positive lead on the battery terminal.
Connect the voltmeter negative lead to the accessory terminal of the ignition switch.

The voltage drop should not exceed 0.3 volts.

If the voltage drop is greater than this value, the ignition switch or associated wiring may be defective.

Resistance Wire Test

The ignition resistance wire controls voltage supplied to the ignition coil during engine operation.

To test this circuit:

Connect the voltmeter negative lead to the battery terminal of the coil.
Connect the voltmeter positive lead to the accessory terminal of the ignition switch.

The voltage drop should not exceed 6.6 volts.

If the voltage drop is greater than this value, the resistance wire must be replaced.

Coil to Ground Test

A coil-to-ground voltage drop test checks for resistance within the distributor grounding circuit.

Excessive resistance may occur at:

Coil to distributor wire
Breaker points
Breaker plate
Distributor housing ground

The voltage drop should not exceed 0.1 volt.

Starting Ignition Circuit Test

The starting ignition circuit can be tested by connecting a voltmeter between the battery and the coil while cranking the engine.

Disconnect the distributor high-tension lead and ground it while performing the test.

The voltage drop during cranking should not exceed 0.1 volt.

If the voltage drop is excessive, clean and tighten electrical connections or replace faulty wiring.

Ignition Coil Testing

Ignition coil tests may be performed with the coil installed in the vehicle or on a test bench.

Typical tests include:

Coil heat test
Secondary winding continuity test
Coil capacity test

A coil may function normally when cold but fail after reaching operating temperature. Heat testing helps identify this condition.

If a coil fails any test, it should be repaired or replaced.

Resistance Wire Replacement

If the primary resistance wire is defective, it must be replaced according to the recommended service procedure.

Replacement involves:

Cutting the brown wire and the red wire with green band at the quick disconnect.
Installing a replacement resistance wire with proper bullet connectors.
Routing the wire through a grommet installed in the dash panel.
Connecting the replacement wire to the ignition switch jumper lead.
Removing the defective section of resistance wire.

The resistance wire must not be spliced, as this will affect ignition system performance.

Secondary Circuit Faults

Loss of energy in the ignition secondary circuit may be caused by:

Fouled or incorrectly adjusted spark plugs
Defective high-tension wiring
High voltage leakage across the coil, distributor cap, or rotor

These problems often produce symptoms such as:

Misfiring
Rough engine operation
Poor acceleration
Hard starting

Inspection and replacement of defective ignition components will restore proper ignition performance.

Safety, Copyright and Source Notice

Safety Disclaimer
Working on motor vehicles involves mechanical and electrical hazards. Always disconnect the battery when servicing ignition components and ensure proper safety procedures are followed. If unsure about any repair procedure, consult a qualified mechanic.

Source
Information compiled from period factory service literature.

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