Here's a quote from
Dan's On Line Motorcycle Repair CourseIt is no substitute for the correct repair manual for your bike, but gives some sage advice on a lot of topics.
Quote:
Ignition coils. Measure the resistance between the primary (low-tension) wire and ground or ground terminal. It should be very low. Like .5 to 1.5 Ohms. The primary wire is the small wire going to the CDI box or points. Next measure the secondary (high-tension) wire and ground. (Note that on most bikes these days, the coil mounting bar, that passes through the coil and mounts it to the frame, is the ground for the coil primary and secondary wires.) This should be quite high, like 6000 to 13000 ohms. If the coil is out side the specs given in the shop manual the coil might be bad. Sometimes, a coil will work OK when cool but fail when it warms up. Let them cool and they work again.