A direct voltage adapter, or peak voltage adapter, lets a multimeter measure the peak voltage coming out of a primary coil and a pulse or trigger coil. That's an important step in diagnosing an outboard, since it's hard to tell how good the spark is, or where the problem is if there's no spark at all. In this video I make one: a simple circuit that's quick to put together and much cheaper than a commercial one. The capacitor is 22uF 400V, R1 is 300 ohms and R2 is 1M ohm. Faulty CDI unit shows it in use.

To test a CDI unit's output, R1 has to be bypassed so the capacitor charges quickly enough. This short follow-up changes the adapter so R1 can be bypassed when needed.