Did You Know: Spark Plug Resistor Caps


Premature timing chain failure/crankshaft reluctor ring movement


  • Engines equipped w/Spark Plug Resistor Caps


The GoTech technical services team receives many inquiries on resistor caps and how to install them correctly. Most automotive applications do not use resistor caps, they are primarily used on motorcycles and power sport applications as well as some modified engine applications.

Resistor caps are intended to be used when the spark plug for the engine application does not have an internal resistor. Resistor caps are designed with many different characteristics to include resistance value, length, angle of projection, ignition wire size. Some resistor caps even have molded handles for applications with the room for easy removal and installation. They can be made of silicone rubber or phenolic resin and can accept various spark plug terminal nut designs. There are also waterproof ends for marine or extreme duty engine applications. To make the correct selection of a resistor cap you will need to know all the characteristics and spark plug specifications as well as any clearance needs that your application may require.

When installing a resistor cap to the wire make sure to lay out your wire to ensure proper routing and length.  Once the correct length has been established cleanly cut the wire with a sharp tool. When reusing your old wire trim the end to make a fresh mating surface to ensure proper connection while making sure not to trim the wire to short. Push the resistor cap onto the wire and then turn the cap like a bolt in a clockwise direction until the cap is tight on the wire. The resistor cap terminal has a sharp point with threads on the outside that will pierce into the core of the wire making a solid secondary circuit connection.  Do not use any sealing agents or lubricant when installing a resistor cap. The below photo images provide a visual of the sealing and connection terminal

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