variable voltage....

[mavis cruet]

i fitted a bmw analogue v.meter a while back and the needle oscillates madly when riding with the headlights on. wavers a bit with the sidelights and pretty steady with no lights. i tried connecting it straight to the battery and it still oscillates but not so wildly. ive tried a digi multimeter which varies a bit, but i dont think the display is quick enough to register the voltage change (i manually disconnected, reconnected it quickly and it gave a similar reading). i get the impression that vibration is a triggering factor.
now, my non electrical mind assumes that something in the lighting circuit is shorting the charging circuit. does this sound possible, and if so any ideas where to start the hunt?

cheers in advance...

karl

 

[John Armstrong]

Could it be a diode out on the diode board?

IIRC there's number of paths to smooth out the phases and so you see a "steady" voltage. One of the paths out would muck it up and cause pulsing of the voltage. On my 100GS I have the voltmeter connected effectively to the battery, and there's no pulsing even with all the lights on.

Best look here: http://bmwmotorcycletech.info/techindex.htm and about 1/3 way down for some real opinions