Plug Wires: Build Them Right



Spark plug wires are the arteries of your hot rod; Providing a path for electrons to flow to the spark plug and creating a spark across the plug gap to initiate the combustion process and power stroke. If this path is ever interrupted, a misfire will occur, robbing your engine of power and creating driveability issues that will drive you crazy.



It doesn’t matter if you’re running a distributor or coil-per-cylinder ignition system, plug wires have a lot of external forces working against them. They live in a brutal environment of extreme heat, they’re whipped around from underhood air currents, have oils spilled on them and during tune-ups, they get yanked and pulled around. All of this while carrying thousands of volts to the plugs.




When shopping for wires, you’ll find a lot of custom-fit applications that are based on the factory routing of the wires, as well as the boots. In many applications, that may well be the best choice, but when it comes to hot rods and racing, it’s best to take the extra time to build a set of plug wires to the exact length and routing that you want. 


MSD offers several universal wire sets that come with the spark plug terminal and boot already installed but have the other end loose so you can cut each wire to your exact length. (These are extremely helpful in remote-coil applications.) They also supply a Mini-Stripper-Crimper tool that guides you through the stripping of the sleeve and provide consistent crimping of the terminal to the wire. Building your own wires will take a little extra time, but it’s worth it in the end to have the right length and routing of the wires for your application. 


1. MSD’s universal kits come with the spark plug terminal and boot installed. Terminals and boots are supplied for both HEI caps and the old style socket caps. Our kit uses the multi-angle straight boot at the plug and is supplied with an HEI or socket style for the distributor cap.


2. The top two terminals, a 90° HEI and a multi-angle terminal, feature a unique dual crimp design. These feature a set of crimp tabs for the conductor and one for the wire sleeve. The bottom terminal is a standard socket type.


3. Universal kits are supplied with a Stripper-Crimper tool that are used in a vise to produce a secure crimp.


4. Depending on which terminal you’re using, the sleeve must be cut off so the conductor can be in contact with the terminal. If a standard terminal was being used, the wire would be pushed flush to the end of the tool.


5. Align the large crimp tabs around the sleeve and the conductor is positioned between the smaller crimp tabs. Sometimes it is helpful to use pliers to bend the big terminals over a little before positioning the assembly in the stripper-crimper.


6. The stripper-crimper has two tabs that should be positioned on top of the vise. With the terminal and wire assembly positioned, slowly tighten the vise until it stops. This produces a factory-like crimp!


7. With the sleeve crimped, use a pair of needlenose pliers to crimp the smaller conductor tabs. Make sure the conductor is pushed down between the crimp tabs then crimp the tabs over the conductor.


8. If you’re using the standard socket terminal, the conductor must be bent and positioned between the terminal surface and the sleeve before crimping it. Use the same steps with the stripper-crimper tool.


9. Universal kits are supplied with these handy cylinder indicator numbers. They simply slide into place on each wire.


10. The supplied stripper-crimper tool works well for a set of wires, but if you plan on building more wires down the road, consider a set of MSD’s Pro-Crimp Pliers. This useful tool will strip and crimp both the sleeve and conductor. Plus, MSD offers dies for other types of crimps such as Weathertight, Deutch an Amp style terminals.


11. Next step is to install the new boot over the terminal. You can use a shot of lithium grease in the boot to help installation, or go with Spark Guard which adds a bit of spark isolation and helps with the terminal connection.


12. The socket style boot needs to be slid over the terminal assembly, with the Spark Guard applied lightly to the inside of the boot pull firmly sliding the boot up over the terminal.


13. With the boot in place, use a pair of pliars to bend the terminal to the 90* position locking the boot in place.


14. It’s always a good idea to measure the resistance of each new wire before installing them. This simply confirms a good connection from terminal to terminal. The 8.5mm wire is rated at about 50 ohms per foot, so a three foot wire should be around 150 ohms. Our wire was about 3.5-feet.


15. A useful feature of MSD’s multi-angle terminals is that they can be bent and retain their position. This is useful when a slight bend is needed to achieve the best clearance.


16. Universal wires will take a little extra time to make, but the benefit is having the exact length and position for your engine and exhaust system.


17. A set of wire separators are always a good idea. MSD’s handy Pro-Clamp separators will hold two, three or four wires and can be mounted to secure the wires from heat sources.


18. Here we see the Pro-Clamp separators slid onto the new wire assembly, these will be secured in place once installed onto an engine.


19. For added protection, MSD offers a roll of Pro-Heat Sleeve that can be installed on the wire to provide extra protection from heat. Heat shrink cylinder indicators are also available.


20. A little heat shrinks the numbers down snug on the wire or can be used to seal the heat sleeve to the wire as well.






Plug wires have their work cut out for them. When there are no problems, the wires are forgotten and may go without being inspected or replaced over time. Depending on your application and what ignition system you are using, the plug wires should be considered a routine maintenance item. This is especially true of the coil wire as it works up to eight times more than the other wires.


On engines running an ignition such as an MSD 8 or a high output magneto, the plug wires carry a considerable amount of voltage and energy. Just like any other part of a race car, the wires will wear. Resistance could go up, cracks or breaks in the conductor could occur, and the terminals will wear from being pulled off and on during pit thrashes. How often you change your wires depends on how often the car is raced. In extreme conditions, you’ll want to inspect the wires every couple of events. For bracket cars and sportsman racing, maybe replace the entire wire set once throughout the year.

Original article by: Todd Ryden | 12/02/2019