@seattle##gs here are some tests you can do.
First test the rectifier circuits.
The regulator/rectifier must be disconnected from everything on the bike.
Set your multimeter to continuity or resistance (when you cross the positive and negative leads, your meter will beep or read zero)
Test One
- Attach your red multimeter lead to the red lead of the regulator/rectifier
- Attach the black multimeter lead to one of the yellow leads of the regulator/rectifier
- Your multimeter should not beep, or give any reading
- Do the same for the second yellow lead (and third if you are testing a three phase unit)
Test Two
- Attach your black multimeter lead to the red lead of the regulator/rectifier
- Attach the red multimeter lead to one of the yellow leads of the regulator/rectifier
- Your multimeter should beep, or give a reading - write down the value on a piece of paper
- Do the same for the second yellow lead (and third if you are testing a three phase unit) write down the value each time
Test Three
- Attach your black multimeter lead to the black lead of the regulator/rectifier
- Attach the red multimeter lead to one of the yellow leads of the regulator/rectifier
- Your multimeter should not beep, or give any reading
- Do the same for the second yellow lead (and third if you are testing a three phase unit)
Test Four
- Attach your red multimeter lead to the black lead of the regulator/rectifier
- Attach the black multimeter lead to one of the yellow leads of the regulator/rectifier
- Your multimeter should beep, or give a reading - write down the value on a piece of paper
- Do the same for the second yellow lead (and third if you are testing a three phase unit) write down the value each time
All of the values above zero that you have written down should be more or less the same.
If there are any wildly different numbers, it signifies a fault with one of the diodes. This is not serviceable, do the unit must be thrown away.
Now test the regulator circuit.
This should be done on the bike, with everything connected - no easy bench tests without more advanced test kit I’m afraid.
You need to have a good battery attached, as the regulator/rectifier will not give a steady output on it’s own, and the battery will smooth out your measurements, making it easier to see what’s going on.
Set your multimeter to DC volts, put the red lead on the battery positive terminal, and the black lead on the battery negative terminal.
- With your engine switched off, and no consumers like coil or lights drawing any power you will see around 12 to 13 volts (varies depending on the type of battery you have)
Lead acid (including gel, AGM, flooded and drycell) are 2.1 volts per cell, so you should see 12.6 volts at rest
Lithium based (including lithium-ion, lithium polymer, LiCoO2, lithium cobalt oxide and LiFePO4) are 3.6 volts per cell, so you should see 14.4 volts at rest
- Start your engine and let it idle.
You should see the voltage at the battery drop to around 11 to 12 volts
This shows that you are drawing more out than you are putting in - absolutely normal for the charging system of this era, and one of the reasons that the three phase alternator came along at a later date
- Now hold your revs at an RPM of three to four thousand
You should see the voltage reading on your multimeter go up to around 14 to 15 volts
Hope this helps!