How to Find Out Which Spark Plug Wire Goes to Which Cylinder

How to Wire an HEI Distributor Cap

1. Connect the primary wires to the HEI distributor, via a plug that snaps into the distributor cap.
2. Insert the spark plug wires in the proper order on the distributor cap.
3. Locate the distributor’s rotor button under the cap and determine its direction.

HEI stands for “High Energy Ignition” or, Electronic Ignition. It can replace “points type” ignitions. This covers a broad range of automotive manufactures and companies that make this type of distributor system. When American Autowire refers to HEI, we are referring to GM 1974 – 1980 Large Distributor Cap design*.

1. Obtain the firing order for your vehicle. You can find the firing order in your vehicle’s owner’s manual or in a repair manual for your specific vehicle.
2. Find the cylinder numbering.
3. Number the terminals on the distributor.
4. Route the No.

You can determine if it is 180 out by removing #1 plug and placing your finger/thumb over the hole. (Temporarily remove the wire from the coil first) Have someone “tap” the starter and you will feel pressure trying to to blow your finger away. This is the compression stroke. Note the direction of engine rotation.

Excessive or unusual engine noises Your vehicle may make some very strange noises if the distributor rotor and cap are malfunctioning – specifically because the cylinders will try to fire but fail. You might hear a tapping, clicking, or sputtering sound when the distributor rotor and cap are failing.

The distributor cap and rotor can only fit one way onto the distributor. If the distributor remained in the engine, there is no problem. If you remove the distributor from the engine and do not mark its position, then you crank the engine until #1 piston is at Top Dead Center, then install the the distributor.

What can a bad distributor cause? Since the engine needs that spark to run, a bad distributor can result your car stalling when it idles. Your engine is misfiring: If the distributor isn’t providing enough juice to the spark plugs, it can cause your engine to misfire, which typically feels like the engine is stumbling.

When the firing order is wrong or delayed, the engine does not run properly. The spark may be delivered to the cylinder when there is no fuel/air mixture or before it is properly compressed. Turning the ignition does not start the engine.

Sometimes, the issue is a slight buildup of carbon inside the distributor. This carbon trace can conduct electricity that affects performance. It could short out the coil voltage and cause a faulty connection inside the terminal of the distributor cap. The result is a misfire in the spark plugs.

Shaking or vibration may be caused by many different things such as faulty spark plugs, poor fuel pressure or misfires. Other things such as a faulty idle air control valve may cause the engine idle to drop below the normal idling RPM which may also cause the motor to shake or vibrate more than normal.