The Best Way to Not Mix Up Distributor Cap Wires

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    How the Problem Could Occur

    • Everything about a tuneup is quite straightforward: You take out a spark plug and replace it with a properly gapped one with the same number; you replace the air filter and fuel filters with the specified replacement; and then you tackle the distributor cap and rotor.
      The distributor cap sits atop the distributor, which may be located on the top front, top rear or side of the engine. The cap is held to the distributor by spring clips or small screws. The distributor cap, in conjunction with the ignition rotor, which is underneath the cap, serves as the distribution point for the ignition voltage in its travel from the ignition coil to the various spark plugs.
      At regular intervals suggested by the vehicle maker, usually from 30,000 to 100,000 miles, the cap and rotor must be replaced because the terminals on the inside of the cap erode away, which results in poor engine performance. This requires that the ignition wires be removed from the cap, and this is the time when a problem could inadvertently be caused by the installer. The ignition wires, which depending on the number of cylinders the engine has could number from four to eight, plug into the top of the distributor cap. The wires sit in the cap in a particular order, called the firing order, and must be plugged into the correct terminal on the cap. Mixing the wires up means the spark plugs receive ignition voltage in the wrong order. When this happens, the engine runs poorly, if at all, so care must be taken to keep the wire order straight.

    How to Avoid a Mix-up

    • There are two ways to keep the placement of the ignition wires correct. The best is to replace the wires one at a time if space allows. Next best is marking the wires as you remove them from the old cap.
      Marking the distributor cap wires must be done in a manner that will be easily read when it's time to plug them into the new cap. A black marker is not a great choice for this because, though legible when the ink is wet, the ink dries to almost the same color as an igntion wire, making the marks very hard to see. Using a paint marker is better, but the paint takes a fair amount of time to dry and can be swiped off the wire accidentally.
      When you have room to use it, a good marker choice is simple masking tape. Simply write a number on the tape with a marker, and then cut the tape long enough to wrap around the wire and then stick to itself to form a tag. Knowing the actual cylinder numbers isn't important. You can use any numbering scheme you like as long as you know what that scheme is when it comes time to plug the wires in to the new distributor cap.

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