The coil is a part of the ignition system of a vehicle. The coil has two windings, the primary winding and the secondary winding. They refer to the two sets of wires inside the ignition coil. The primary winding gets the electricity from the battery, while the secondary winding transports this electricity to the distributor. If any part of the coil doesn't work properly, your car may not start at all.
You can do coil testing on your own. Be careful. Keep your hair, skin and clothing away from the any part of the ignition system, which can produce a LOT of electricity. Ask a friend to help you out.
Conduct a visual inspection of the ignition system. You might spot immediately what is wrong with the system without having to actually test your coil. After making sure that there are no sparks flying about, you may proceed. Always use insulated pliers while you're doing the test.
The test will check if the ignition coil produces sufficient sparks. You must first disengage the output wire of the ignition coil. Use a spark plug to connect the end of this wire to a ground wire. Inspect the spark plug and locate its threaded part. Attach the ground wire to this part.
Now look for the negative terminal of the ignition coil. There is a ground wire connected to this terminal. Disconnect this. Attach a ground wire to the terminal.
Ask your friend to turn the engine on. Look for a good grounding point in the engine. It would be best if that grounding point is near you, to provide easy access. Any metal can be used for this, even the engine itself. Use the ground wire of the ignition coil and touch the grounding point with it.
Observe the sparks that are produced while you tap. If you get a bright and visible spark, your ignition coil is working properly. If you get a weak spark or if no spark is produced at all, it usually means that something is wrong with the secondary winding of your ignition coil.
To confirm that your coil is in good condition, you can also conduct a test to check the resistance of your ignition coil. The most usual way of doing this is through the use of an ohmmeter, which measures ohms. An ohm is a unit which will show the amount of electrical resistance between two conductors. All the wires connecting to the coil must be disconnected before you start the test.
Check first the resistance between the side terminals of the coil. Refer to your car manual, to know the specific values referring to resistance using an ohmmeter. Afterwards, check the resistance between the center terminal of the coil and a side terminal. Any of the two side terminals will do. If the resistance shown is significantly different from the values stated in your car manual, the ignition coil is not functioning properly. You can also ask help from your mechanic in reading the ohmmeter.
Test your coil regularly to ensure the smooth operation of your car's ignition system.