In the dark ages of motorcycling, shop mechanics relied on resistance tests for checking out ignition components, specifically the ignition coil and its partner the pulse generator (or trigger). However, ohmming has never been a good way to test an ignition coil and it's no better a method for a pulse generator. Savvy techs learned to test both of these parts dynamically, that is, while they were working. The ignition coil by simply rapidly powering it on and off, and the pulser by connecting to it an analog multimeter set for uA (pico amps) and watching for a subtle needle twitch. Kind of a homemade megger. Much better than ohmming, officially endorsed by the Yamaha factory, and the method I prefer even today. An even more advanced method of testing a pulser is to use a 9v battery to substitute for the pulser, attaching it in the bike's harness. Very effective, and I sometimes use it as a backup to the twitch test. But these comparatively, innovative, alternative, and though uber-effective rather guerrilla mechanic methods have never been widely known, so another method eventually came to the fore, one endorsed by all manufacturers and now included in the current OEM manuals. This is the peak volt test.

You'll recall that the ignition coil's two windings-- primary and secondary-- cross induce. That is, after the primary has induced the secondary, the secondary in turn reinduces the primary, and the two actually go back and forth, until the energy is spent. This backlash effect back to the primary is very predictable and some geeky wag somewhere came up with the idea of testing the health of the whole ignition circuit by measuring it. Today's OEM manuals list voltages that can easily be read at the primary of between 150 and 300 volts. A reading that is out of range of the manufacturer's published spec will indicate that further tests to pinpoint the trouble need to be performed.

Interestingly, the peak volt test's greatest contribution from the standpoint of learning, is that it is a direct indicator of the speed of the primary winding's collapse, and thus the condition of the transistor inside the spark unit. When collapse is sharp, the transistor's break is clean. The peak volt test then, aside from its diagnostic value, is the best indicator of the spark box's function. It's a verifier of the speed of collapse.

Get a peak volt adapter (designed for digital multimeters) made by a very innovative American company called ESI on Amazon. The Big Four also sell their own version, made by Kowa in Japan.