How to Wire an Engine Coil

by William Kinsey

An engine coil is used to produce the high voltage needed to fire the spark plugs on an internal combustion engine. Coils on older model cars -- or those made before 1980 -- were controlled by a mechanical switch commonly called points. Later model cars have the coil controlled by engine electronics. Most coils have three or four terminals. Two terminals power the primary coil and the other terminal or terminals provide the high voltage from the secondary coil. The two primary terminals are usually labeled positive and negative.

Step 1

Check the engine repair manual for your make and model car before beginning work. Locate the positive coil wire, which runs from the ignition switch to the positive terminal of the ignition coil. On later model cars, this wire may run back to the car's computer or the ignition control module.

Step 2

Connect the positive coil wire to the positive terminal of the ignition coil. Locate the negative coil wire. On most cars made before 1980, this wire connects to the points switch, which is located on the distributor. The distributor connects all of the spark plug wires. Most newer cars do not have a points switch, so that terminal is connected to ground or the negative terminal of the battery.

Step 3

On vehicles made before 1980, connect the points wire to the negative terminal of the coil. Plug one end of the high voltage spark plug wire into the high voltage terminal on top of the coil. Plug the opposite end into the center high voltage terminal of the distributor cap.

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