We’ve all done it. Every mechanic, whether a professional or a weekender, has removed the spark plug wires from the plugs, distributor, or controller and then realized they aren’t sure which ones went where.

“Was it 1-3-5-2-4-6 or 1-4-2-5-3-6?”

This happens more often than most of us will admit.

Most vehicles have the firing order mapped on one of the small “circuit” maps at the radiator mount or under the hood. Until recently, this was the norm – a sort of unwritten convention. Now, though, many vehicles don’t include any schematics at all outside of the owner’s manual, which themselves are increasingly getting less and less technical.

So knowing your engine’s firing order before you pull wires or change plugs is a good idea. Labeling wires before removal or, better, removing them one at a time for replacement is always the best course of action.

Of course, many newer cars don’t have spark plug wires at all – at least not in the traditional sense – and have individual solenoids above each plug in the line. This simplifies matters, but you still have to know which one goes where. Rarely do manufacturers label the caps or wiring or even the cylinders on the heads.

For example, a 1990 Toyota pickup truck with a four cylinder engine has embossed numbers for each cylinder molded into the heads, but a 2012 RAV4 with a four cylinder engine does not have them labeled. Even on an inline four, it’s sometimes hard to remember if cylinder 1 is at front or back. Make it front wheel drive so the engine is turned sideways and it can be even more confusing.

So the moral of the story is this: always label your wires and always know your engine’s firing order. Whether it’s your car or a car you’re just working on for a friend (or professionally), you should know that firing order.

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An automotive enthusiast for most of his adult life, Aaron has worked in and around the industry in many ways. He is an accredited member of the Rocky Mountain Automotive Press (RMAP), the Midwest Automotive Media Association (MAMA), and freelances as a writer and journalist around the Web and in print. You can find his portfolio at AaronOnAutos.com.

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