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Hey Guys, my r100r has about 24k miles on it. The Gen light will just randomly come on and then go out. It is totally random and sometimes comes on at 2k rpm, or after I get off the parkway. Short in diode board? Any ideas?

I had to replace my alternator rotor with less than 20k on it.
My symptoms:
No GEN light with switch on but motor not running
light would start to glow at 2.5I

Centripetal force and where the break in the rotor wire is changes where these symptoms occur. Luckily for me, the lack of the GEN light when the motor wasn’t spinning made diagnosis easy as there was no continuity between the rings of the rotor. If the continuity breaks only when it’s spinning, it’s tougher to tell. I guess you can pull the wires from the brushes and test the resistance as the engine revs to different rpm.

Be careful with the bulb holder...the delicate foil can break, creating more problems...it's no longer available from BMW. Fortunately, there's an aftermarket replacement. She and her husband, Airhead owners, decided to build a replacement. It's getting good reviews.

http://katdash.com/

Kurt in S.A.

Have you had the front cover off lately? I recently had the front cover off to check the points and found a sizeable mouse nest. I guess while removing it I moved a wire which got pinched while putting the case back on. when I first started it everything seemed fine, but after a few miles the gen light came on. once I got back to the house I removed the front cover and found the chaffed wire.

Thank you for all the response! It does act like a short somewhere. I will investigate when I take off the front cover to fit the Motorrad Elektric ignition when it arrives. Having advance hang up problems also.

Rotor is a common intermittent failure.

Gibson, a current (!) short(!)coming with Boxerworks is that there are no 'Electrical Guru' types posting. I suggest joining and posting your problem on the BM Bikes & BM Riders Club forum. It's UK based and there is a very switched(!)on Scottish bloke using the handle 'Galactic Greyhound' who publishes some useful fault finding guides. He has been known to walk people through some quite complicated issues at no charge(!).

Best of luck getting it sorted.

Good advice Charlie.
You could tack onto the end of this thread Gibson...
http://www.bmbikes.org.uk/Forum/viewtop ... 9c01fb0d67

Wish you had mentioned a year model.

► The mechanical regulators on 70's and 80's bikes often have issues due to dirty internal contacts. These can be easily replaced with a modern solid state regulator for under $25, which has no internal contacts. This same Bosch regulator was used on Saab, Volvo, VW and a slew of other vehicles. Scan Ebay for "Bosch regulator" such as #272655228783. Heck, even NAPA sells a replacement.

► Surely a short circuit would have fried a wire or blown a fuse by now. Sounds more like an intermittent connection. After 30 years of rain and washing it's possible for even good connections to get "iffy". You might try adding a dab of anti-oxidation compound (such as No-Ox-Id) to each electrical connection, starting with the charging system connections.

It most probably does NOT have anything to do with the GEN indicator lamp in the gauges. If the lamp comes ON, then it's working as it should.

► Check the condition (length) of your alternator carbon brushes. Once the brush wears to a certain length, the spring pushes on the plastic corral for the brush, instead of adding pressure to the brush. Low spring pressure can cause intermittent alternator output.