1989 R100G/S Charging System Problem

[Lentulo]

I recently began diagnosing a problem my BMW developed involving the charging system. The charging light, over a 1 to 2 month period, began staying lit until reaching a higher RPM when I first began a ride. Using several sources, it appeared to be a bad rotor, which I replaced. I also replaced the original voltage regulator with the Police version, since I tend to use my bike more for short, around town trips.
Since replacing these parts, I started rechecking everything. I did find 12V at the alternator brush terminals with the key on but bike not started. I then, with the multi-testor attached to the brush terminals, performed the next test of the alternator and found that the voltage dropped only to 5V, but not until reaching 5000 RPM. I performed this test 2 times with the same result.
Afterwards, I now do not have a reading over 2 V at the alternator brush terminals. I checked again with the original regulator, plus with a jumper of the regulator plug. All 3 checks showed the same voltage reading.
Since I had another battery (gel type) in the garage, I installed this as well and found that it had a much quicker recovery with the plug-in charger after turning the key to the on position to check voltage at the brushes.
I also have 12V at the diode board. All connections seem to be together.
I could not find any other info on the Airhead website.
Would anyone have a clue as to what I should try next?
Thanks!!!

[pmdave]

Can we assume you have a copy of the charging handbook from Motorrad Elektrik? Charging system failures are the Achilles Heel of airheads of all models.

With the stock system, it helps to add additional ground wires from the diode board to the engine block, to ensure a good ground. There are a number of other little fiddly things, such as checking brush length, cleaning contacts (such as the red wire at the starter solenoid), and occasionally replacing the 3-wire bundle that connects the alternator to the diode board. Check all the connections at the starter protection relay that relate to the charging system. And dig around in the headlight bucket and make sure all the connections there are clean and tight.

Some systems seem to work better than others, and some just never work right. I got so tired of the weak, troublesome system on my 1980 R100 that I yanked it out and installed the Omega 400W kit. And, being a little paranoid, I also added a separate charge light with an easily replaceable bulb, that is hard wired to the regulator, not through the instrument cluster connections.

pmdave :thumb

[Lentulo]

Thanks to all viewers of my problem...
I finally built a test light and discovered that the original diode board had 3 of the 6 large diodes to be bad. I replaced it with an Omega from Mororrad Elektrik and, like magic, my charging light now is not lit at idle speed of about 1200 RPM.