Here is the best practice charging system troubleshooting method. This is the professional way. Do it in order and think about the logic.

1. The first step is a visual inspection of the wiring harness and its connectors. Not only are eighty percent of electrical system troubles traceable to connections, replacing the vintage Honda wiring harness has solved many charging and ignition system issues. At the very least, the handful of canon plug connectors need to be rebuilt on a 40-50 year old Honda.

2. While inspecting, take a look at the alternator brushes and the keyswitch. Very worn brushes will affect charge. The keyswitch should feel precise when it is turned on and off. If mushy-feeling, or if the switch bottom is loose, the switch needs to be replaced. If it is an aftermarket switch, I would replace it even if it does not show signs of trouble. Replace it with a factory switch (even a used one if necessary), not an aftermarket.

3. Do not base any determinations on your onboard voltmeter. The factory voltmeter is inaccurate. Use a multimeter, analog or digital, but one that has a 10 or 20 amp jack.

4. Inspect your battery. Don't skip this (I know you want to)! If a wet-cell type battery, top off its water and after bench-charging (the charger must be a 3-5 amps or better--forget "trickle" or "tender" chargers), specific gravity test (1.250) then load test. If a sealed battery, after charging do an open circuit terminal test (13.5VDC minimum) then load test. The load test is done using a 100-watt, 2-ohm load resistor available at electronics supply houses for about $40. Connect the battery to the load resistor at one of the outer lugs and the center lug. Connect a multimeter also. After 15 seconds the battery must not drop below 10 volts. If it does, recharge it and retest. If it fails again, replace it no matter what. Even if new.

5. Now it's time to confirm the problem. Set up your multimeter for a 10 amps range. It must have that capability. Remove the bike's mainfuse and put the meter in its place. Momentarily turn the keyswitch on and if your multimeter reads negative (backward), that's good. If not, reverse the leads.

6. Start the engine and rev it to 5,000 rpm, and after quickly reading the meter, let go of the throttle. You don't want to hold the rpm because that will make the regulator cut charge. If you read 5 amps or more (you'll usually see as much as 7-8), the charging system is working fine.

7. If less than 5 amps, bypass the regulator by jumpering the battery's negative terminal to the white wire inside the canon plug (via a paper clip--don't separate the canon plug). Repeat the charge test, this time staying below 3,000 rpm. If the regulator bypass makes a huge difference, replace the regulator. If the jumper got uncomfortably hot, threw sparks or melted, the alternator rotor is bad. Replace it. In this case a quick resistance test of the rotor will confirm the failure.

8. If the bypass didn't change anything, remove the jumper and dangle a paper clip or feeler gauge on the tip of a pencil three inches from the alternator cover. Turn the keyswitch on, then off, then on again. Do not start the engine. Each time the key is on, the feeler gauge should "kiss" the alternator. If it does, magnetism is confirmed, as is the rotor's whole feed circuit.

9. If it doesn't, do a volt drop test from the battery positive terminal to the alternator's positive brush. Do it right at the brush, not at the canon plug. The positive brush is the outermost one. Turn the keyswitch on. Your reading should be under 1 volt. If you have maintained your wiring harness connectors and/or replaced the harness, it will be far below 1 volt. If more, repeat the test at each break in the circuit (using the factory schematic) until the reading goes below 1 volt. The last juncture (connector) will be the problem.

10. If so far everything checks out good, disconnect the large alternator canon plug--the one that contains three yellow wires--and using a terminal disassembly tool, extract the three terminals having yellow wires from the alternator side of the connector, and reconnect the connector. Set your multimeter up for 50VAC and jumper the load resistor onto your meter leads, using the two outer lugs, then clip the meter leads to any two yellow wires. Start the engine and rev to 5,000 rpm. You should see 18-25VAC. Repeat on another two yellows, and again at another pair, until all three yellows have been tested. If you get less, the alternator stator is bad. If you get 18-25VAC or better, the rectifier is bad. Be sure to retest charge after your repair.