Volts vs. Amps vs. Ohms
As demonstrated in Parts 1 and 2, best practice in troubleshooting vintage Honda charging and ignition systems does not involve an ohmmeter. Static tests are the least reliable and conclusive when it comes to systems based on wire windings.

Your motorcycle’s electricity has both flow and pressure. The flow can be visualized on a test meter in amperes (amps), and the pressure on a meter as volts. Flow and pressure are different things. An amp meter, or “ammeter”, shows electricity working. A voltmeter on the other hand shows only electricity’s static aftereffects. One is active, the other is passive. For this reason, an ammeter is a more faithful measurer of the charging system than is a voltmeter.

Similarly, resistance tests of these parts and systems are not the most conclusive or determinative because they do not duplicate actual working conditions, and while consumer electronics parts fail in ways that are predictable and definitive using an ohmmeter, those in Honda motorcycles really do not. Dynamic testing whenever possible is preferred because it does. Can you get by without using best practices? Sure. And many times you will. Measuring charge in volts is commonplace. However, it is not as accurate as measuring it in amps, which was years ago actually the preferred method everywhere you looked, including in Honda manuals of the 1960s and early 1970s.

There are a number of problems with voltage readings of charge, too many to elaborate on here. But consider the fact that simply, loads, that is, drains, are always measured in amps. No one argues that. But somehow the logical corollary that current merely going the other direction should be measured in the same way—in amps—is rejected and people choose to use volts. It is not even possible to do a charging system breakeven test in volts. It’s not electrical flow. Similarly, testing an ignition coil by checking its resistance is an inadequate, incomplete method. The coil is a wire winding, and as such, as the 95/50 Rule will tell us, it is best tested while it is operating.

The 95/50 Rule
Vintage Honda charging and ignition systems parts are prone to fail in ways that are unique to powersports vehicles. Powersports is a unique world. Thus a proven principle in powersports electrical troubleshooting is that static electrical tests are inferior to dynamic tests when testing any of those parts that are made up of coils of wire. They are not reliably tested with a resistance test. The fact is, a piece of wire hundreds of feet long coated with lacquer, wrapped into a coil and bolted to a motorcycle has a habit of over time losing parts of its insulation and doing crazy things. They have a habit of “lying” to the troubleshooter. When cool and not carrying an electrical load, they can meet factory manual resistance specification. But when stressed by actually working, by carrying current, and thus warmer and undergoing physical, dimensional expansion, it is then that they reveal the truth of their condition. Veteran mechanics have long known and experienced this—it is almost second nature to them. The 95/50 Rule is one that is important to the troubleshooter.

Here’s what the 95/50 Rule means. When the winding is tested with an ohmmeter and it reads bad, then the chances of it actually being bad are 95 percent or better. Okay. That makes sense, and it's conclusive enough to warrant buying parts. It would be best if the part was dynamically tested instead of “ohmed”, but for argument’s sake let’s stick with the resistance test. However, if your resistance measurement of the suspect winding results in a good reading. Well, this is actually a problem. This time the chances of the reading being accurate drop to only 50 percent. The reading is unbelievable, ambiguous, equal to the toss of a coin. Because an ohmmeter does not stress the part enough to accurately test it in light of the kinds of failures motorcycle wire winding based parts exhibit. This is the nature of wire windings on motorcycles and this is where most would-be troubleshooters get into trouble. Dynamic tests are always preferred over static tests.

Powersports wire windings are tested dynamically by actually working them. An alternator stator for example is tested, as explained previously, with a load resistor across its output wires. An ignition coil is tested with a tester having a spark gap several times as large as the standard plug gap to simulate cylinder compression and more importantly to put a strain on the coil and the rest of the system. A rectifier, traditionally tested with an ohmmeter, is actually most conclusively tested while it is working in the system, by comparing the current going into it versus that coming out of it. And a voltage regulator (again refer to Part 2), is most conclusively troubleshooted in a similar way, by noting its effect on charge when it is in the system versus when it is out of the system. A vintage Honda permanant magnet charging or ignition system is most reliably tested without ever resorting to the use of an ohmmeter.

Permanent magnet charging systems part 1
Permanent magnet charging systems part 2