How to Test a Motorcycle Ignition Coil
Testing a motorcycle ignition coil is important especially when you install a new ignition switch. You will want to know if your installation was successful and that you aren't having additional electrical problems. The good news is that you only need one gadget to help you figure this out. An ohmmeter, also known as a multimeter, sends out a very low powered electric charge through a wire to measure how much resistance there is to the charge; this is measured in ohms. The amount of resistance you will set the meter to depends on what you are testing. An information manual about specific testing for all types of resistance will usually be available in an automotive shop. Pick one of these up and head on outside to start testing.
Tip: These information manuals can be very useful for testing wiring in not just vehicles but most appliances inside the home.
Step 1 - Charge the Battery
Make sure your motorcycle battery is fully charged. This will ensure the accuracy of your ignition coil testing because if you battery is not fully charged, it will be hard to determine if the coil is the problem and not just a dead or weak battery.
Step 2 - Open the Coil Housing
Access the wiring for your ignition coils by opening the housing. First, turn of the engine ignition switch and make sure the ground cable for the battery is disconnected. Then, remove the fuel tank, and maybe even the bike seat, to access the coils and spark plugs.
There are some motorcycle models that will have the ignition coil be self-contained and located right under the flywheel, meaning this and the ignition starter coil are one in the same. However, it's mostly mopeds and small European bikes have these types.
Step 3 - Remove the Plug Cap
Remove the plug cap for the test. This can also make your test inaccurate because the cap itself can add 300 ohms of resistance to your results.
Step 4 - Get the Resistance
Measure resistance between low-tension, or primary, wire and ground terminal wire. Your result should be very low around 0.5 to 1.5 Ohms. If you are not sure about which wire the primary is, it will be the small one going towards the CDI box or CDI points.
Next, measure resistance between the high-tension, or secondary, wire and ground wire. This result should be high around 6000 to 13000 ohms.
Step 5 - Study the Results
If the resistance between these wires is outside the indicated numbers, then it is likely your ignition coil is bad. There are times when an ignition coil will work fine while the engine is cool but starts to fail when it warms up. If you are willing to spend a little more, there are machines that can test ignition coils under pressure.
Step 6 - Test the Coil
Another simple test you can do, regardless of the type of coil you're dealing with, is to check the voltage flowing with battery connected. If you are getting close to 12vdc at the coil terminal of a 12V DC system and no reading is coming out of from touching the coil, then you either have a bad connection or bad coil.
Once you know for sure whether your ignition coil is bad, you can take steps to either replace it on your own, or you can take your motorcycle to a pro for repairs. Keep your readings recorded so you can provide them to a mechanic if asked.