How to test spark plug wires without a multimeter

Spark plug wires transfer thousands of volts to spark plugs up to 45,000 volts, depending on requirements. They have strong insulation and rubber boots on each end to prevent excessive voltage surge from the wire before it touches the spark plug.

Spark plug wires work in harsh environments and they can break at any moment, exposing the spark plugs to little or no spark. Thus, learning how to quickly test spark plug wires will be useful, especially without multimeters. 

Step #1: Turn off the engine and inspect the spark plug wires.

• Inspect wires or cases for physical damage such as scratches or burn marks. Inspect the spark plug wires and the cover above them, known as a boot, with a flashlight or in a well-lit area. This will be a series of wires running from the cylinder head to the distributors or ignition coils at the other end. As the wires come off the spark plugs, look at the insulation around them. (1)
• Inspect the area between the boot and the spark plug and coil for rust. Loosen the top spark plug boot and check where the contact is made. Inspect for discoloration or deterioration. Carefully remove the spark plug and look for corrosion or scratches on the underside.
• Check the spring clips in the distributor cap holding the wires in place. Trace the wires from the cylinder head to where they connect to the distributor at the other end. Wiggle the end of the wire to make sure the clips are securely attached to the top of the spark plug. They create pressure that keeps the wire and plug securely attached when not broken.

Step #2: Check with the engine running.

Start the engine and check for arcs around wires or crackling noise indicating a high voltage leak. Do not touch the wires while the engine is running, as high voltage may cause electric shock.

While you're watching this, have someone else turn the engine on. Look for unusual changes such as sparks or smoke and listen for them.

Now consider the signs and symptoms of a faulty spark plug wire. A failed spark plug wire shows obvious signs of wear. The most common signs and symptoms are:

• Random idle
• engine failure
• Radio interference
• Reduced fuel consumption.
• Emission tests failed due to high hydrocarbon emissions or a DTC indicating cylinder misfire. (2)
• Examine the engine light

You can also look for an arc by spraying spark plug wires. Fill the spray bottle halfway with water and spray all the wires. To see if sparking occurs, concentrate the spray on the contacts that connect to the spark plugs. Stop the engine and carefully inspect the dust boots if you find sparks around the spark plug.

Step #3: Using a Circuit to Test Wires

Check if the spark plug wires are routed correctly. See the spark plug diagram in your vehicle owner's manual to help you with this task. Follow each spark plug wire from its cylinder block connections to the corresponding spark plug. Each wire must be connected to a separate spark plug.

This can be a complication if you've changed spark plugs before, especially if the shoe position is incorrect. Crosstalk can cause power leakage, which can lead to motor problems.

useful tips

• Even though your ignition wires have a sheath, some engines use coil-on-plug (COP) setups that completely bypass the spark plug wires.
• To prevent conduction, drain and keep spark plug wires clean.
• Crossing spark plug wires is not necessarily a bad thing. Some manufacturers do this to neutralize magnetic fields.

F.A.Q.

What causes spark plug wire damage?

1. Engine vibration: This can cause the electrical contacts of the spark plugs to slip. The ignition coil and spark plug wires can be damaged if the spark plugs require more voltage to ignite.

2. Engine block heating: High engine temperatures can melt wire insulation, causing voltage to drop to ground instead of to spark plugs.

What happens if the spark plug wire breaks?

If the spark plug wires are damaged, you may experience the following symptoms:

– Engine failure

– Rusty idle

– Failed emission tests

– Problems with starting the car

– The Check Engine Light (CEL) comes on. 

However, these signs can signal a breakdown in other engine components. 

Take a look at some of our articles below.

• How to test a spark plug with a multimeter
• How to check the ignition coil with a multimeter
• How to use a multimeter to check the voltage of live wires

Recommendations

(1) environment - https://www.britannica.com/science/environment

(2) hydrocarbon emissions - https://www.statista.com/statistics/1051049/

China-number-of-hydrocarbon-emissions by vehicle type/