Skip the auto shop - Our mechanics make house calls

How to Replace Ignition Cables (Spark Plug Wires) in Your Car

ignition cables

The purpose of your vehicle’s spark plugs is to ignite the fuel and air available in the combustion chamber. They do this because of a signal received from the computer module or distributor cap.

If the ignition cable, or spark plug wire, carrying this signal fails, the operation of the engine becomes mistimed and under-powered. One or more cylinders will may misfire or weaken. Another result of the fuel and air not combusting completely is a buildup of gases and residue in your injectors or cylinders.

The symptoms of failing ignition cables include rough idling, an illuminated Check Engine Light, and a general lack of engine among others. This all can be very easily avoided with a few simple steps.

Part 1 of 1: Replacing the ignition cables

Materials Needed

battery with red and black cables showing

Step 1: Disconnect the battery. Disconnect the negative battery cable to cut power to the ignition cables.

Disconnect the bolt holding the cable to the terminal using a socket or a wrench.

  • Warning: Set negative battery cable aside so that it will not make contact with anything metal, or a connection may be made restoring power to the cables.

location of ignition cables

Step 2: Locate the ignition cables. The cables will be routed from the spark plugs on the top of the cylinders to the distributor cap or module that powers them.

hand removing spark plug

Step 3: Replace the cables. One by one, remove and replace the spark plug wires.

By doing them one at a time, you will not have to worry about accidentally switching the wires.

To remove an old cable, pull directly upward on the boot of the cable on the spark plug end, and then pull upward on the boot connected to the distributor cap or module. Be sure to only pull on the boot; DO NOT pull on the cable itself.

example of a spark plug wire removal tool

  • Tip: If you are sure you are not going to use the old spark plug cables again, you can use a pair of pliers to help you remove them. The pliers will most likely damage the boot and terminal of the old wires, so it is not recommended that you use pliers on any ignition cables you plan to use again. Otherwise, you can do it by hand or with a spark plug removal tool.

examples of different ignition cable lengths

Again, make sure that the length of the cable you disconnected is the same as the length of the new cable. Extra wire is unnecessary and your engine may not have room to compensate.

diagram of firing order of the cables

What is even more imperative than matching cable length is that you do not mix up the order of the ignition cables. The spark signals are sent in a particular order to each cylinder to time when the piston is at top dead center (at the very top of the cylinder). Improper installation of these cables can result in poor combustion or misfiring of the cylinder, which will cause drivability issues and potentially severe damage to the engine.

  • Tip: If the order of the wires ever gets confused, look up the firing order for your exact vehicle for reference.

example of damaged cables

When removing the spark plug or ignition cables, inspect them for signs of other issues with your vehicle. The most easily detected are signs of burning carbon or oil. This would indicate a failing valve cover gasket and/or failing o-rings around the old spark plugs.

To install a new cable, push the new ignition cable boot on one end to the module, and then push the next end onto the spark plug.

spark plug wire grease

  • Tip: If you wish to use spark plug wire grease (dielectric grease), insert a small drop into the new boot before placing it onto the spark plug.

Move on to the next cable and repeat this step.

Step 4: Reconnect the battery. Reattach the negative battery cable to the terminal to restore power.

Hand tighten the retaining bolt and snug it down with a wrench or socket.

Close the hood of the vehicle once you are finished with this step.

Step 5: Test drive the vehicle. With the car in park, start the vehicle. If the idle is holding steady between 600 and 1,000 RPMs, go for a test drive and observe your vehicle’s drivability.

  • Note: Listen for stuttering, rough idling, and misfires, and feel for any sluggishness.

The ignition system on your vehicle plays a very large role in its operation. Issues with the ignition system are going to slow down and depower your engine. Extended use under these conditions will cause various damages and wear out other parts involved. If you follow the steps laid out in this guide, you can fix these issues and avoid further damage. However, if you’d prefer to have a professional perform this repair, you can always count one of the certified technicians at YourMechanic to properly replace your ignition cables for you at home or at the office.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

Post a question and get free advice from our certified mechanics.

ASK A QUESTION

More related articles

How to Buy Fuel Treatments
Adding a fuel additive to your gas tank when you fill up is one way to clean vital engine parts of deposits, improve the performance of your engine,...
Insurance Requirements for Car Registration in Kentucky
The Kentucky Transportation Cabinet requires that all drivers in Kentucky carry liability automotive insurance, or “financial responsibility” in order to operate a vehicle legally and maintain vehicle...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...


Related questions

Q: Oil leaking into spark plugs galley, car won't start

If you found oil has entered the spark plug tube galley then the oil may have shorted out all the coils and plug wires causing the engine no start. The oil is getting in the galley from a leaking valve...

Q: Car turns over but won't start

Hello! I recommend first having the starting system checked to verify the starter and battery are functioning properly. Both components are vital to starting the car. If either or are malfunctioning it will cause the vehicle to experience a no start...

Q: In mornings when cold and mostly after a rain car will miss very bad and then clear up

Anytime you are getting a misfire when it is damp and cold the ignition system is going to be the cause most likely. The most common cause will be the ignition spark plug wires arching to ground until the moisture...