I reluctantly turned back home recently when my 1985 K100RS charging light began winking.
I have an on-board after market computer that typically shows only about 13.6/13.7v. while underway, yet I've never experienced a battery so flat the bike would not start.  I put the low reading down to error in the instrument's accuracy rather than an alternator that was failing.  When the OEM instrument light began signaling me, I suspected the alternator was indeed bad. I had it rebuilt at an auto electric shop.  Today I rode the bike for the first time with the rebuilt alternator and found, after a heat soak or two, the on-board v. meter reads about the same as it did before I had the alternator rebuilt.  Back home, I used my multimeter (mm) to check voltage at the battery with the K-bike at idle and at 3k rpm.  At idle the warning light glows faintly; at 3K rpm the mm reads around 13.7/13.8 volts.  At that higher reading, the instrument warning light came on very brightly.
My mm is an inexpensive hobbyist model of unknown accuracy.  I decided to do the same charging test on my 1983 R100RS.  The R-bike read 14.1 at 3K rpm.  If I'm not mistaken, that bike is rated at a modest 280 watts, yet it seems to outperform the K-bike!
At this point, I plan to check for parasitic load on the K-bike.  To do that, I would connect my mm between the neg. battery ground cable and the engine with the ignition off, correct?  There are other wires at the neg. battery pole. They should remain connected during the test, correct?
Thanks in advance for any suggestions/insights.

That is all correct so far. Have you had the battery load tested because a bad battery will cause low charging volts due to it taking more than needed but they usually dont last long after they start doing that. 14.1/14.2 is a good voltage.
The clock will draw about 5mA and that is all that should be working when the key is off. If you get much more start taking the fuses out one at a time to see where it is going.

had a similar issue when I changed my regulator

I had to clean up the tang that makes contact to the regulator body contact



but it does sound like the battery ....or more importantly the negative cable to the gearbox is compromised if the regulator is all good

would measuring the battery terminal negative and the gearbox bolt ...or a good earth point some where on the frame ....with volts on the mm scale  and look for voltage drop when loaded up and running

you didn't mention the battery static voltage ( with the bike stopped ) and some load applied ...(turn the headlights on ...but some don't have the off option )  and see what voltage that the battery retains ...  also do the negative battery - earth connection measurement

good luck

brickrider wrote:....
At this point, I plan to check for parasitic load on the K-bike.  To do that, I would connect my mm between the neg. battery ground cable and the engine with the ignition off, correct?  There are other wires at the neg. battery pole. They should remain connected during the test, correct?
Thanks in advance for any suggestions/insights.

Careful you don't blow your DMM. You need to use the 10amp setting first and if nothing then switch to milliampere setting.
Just make sure the only thing that is connected to the neg battery terminal is the black probe from your DMM. You'll need a good connection to get a proper reading.

13.6V or 13.7V is not really charging all that well but as suggested, get your battery tested first because the symptoms to me sound like your battery is on the way out. The charge light glowing brightly while revving indicates a boarderline/dud battery.

The battery sat in the bike overnight and still shows a charge of 12.9, same as yesterday when I checked it. There doesn't seem to be much or any parasitic current draw. I'll try to find a shop that can load test the battery today.
The battery is a Deka 121v. 360 AH if I recall correctly.  It's way less than one year old.  It's always had a good life, having been maintained on a C-teck charger between rides. If it proves faulty, that will be the second battery in a row that's proven to be a bad purchase.  (I had a different brand fail last year and strand me in the New Mexican desert on the airhead).
I doubt these problems can be put down to high resistance in the EME cables.  When I first noticed problems and before I had the alternator rebuilt I went through all the connectors, cleaning and DeOxit-ing and assuring they were snug.
Kapitan, if I understand your recommendations correctly, you say I should remove all the negative wires from the battery save for the ground cable when testing for parasitic current draw.  I don't understand that.  Wouldn't removal of those guarantee no possibility of such a draw?

I think what Kaptain means is the DMM should be in series with all the ground leads that normally connect to the negative terminal of the battery.

12.9 after overnight sounds high  to me 

good to hear you have changed the cables for better

Check your battery terminal connections and the ground on the left side of the transmission to make sure they're all clean and tight.

robmack wrote:I think what Kaptain means is the DMM should be in series with all the ground leads that normally connect to the negative terminal of the battery.  

Correct. I was refering to BR's comment..."There are other wires at the neg. battery pole. They should remain connected during the test, correct?" ... No
Remove all wires/cables from the neg terminal. Black probe connects to the neg terminal. All the wires that came off the neg terminal connect to the Red probe, OR you can test each wire separately as long as the others remain disconnected.

Sounds like a bad battery that's failing under load. Mine did that and the charge light started winking and glowing. Probably a bad cell. Charge voltage looks too low at 13.7ish but that's not necessarily down to your alternator.

I took the battery to a shop today. As I'd stated earlier, it's a substantial battery, under one year in service. It was deemed okay by the shop, having passed the load test at 400 CCA.
I returned home, installed the battery and stated the bike.  It was generating 14.3v. at 3k rpm at that time, so I was encouraged.  However, I'd seen something close to that before, only to have it drop down into the mid-13V. after the bike had run enough to warm things up.  I was pleased, however, to NOT see the idiot light at 3 k rpm this time.
I'll give the ol' girl a proper road test tomorrow and see how she performs. Electrics on the early K-bike can mystify me.

14+V tells you the alternator is doing its job.

Some of the wiring may be getting sketchy.

If you don't want to "waste" time tracking it down then one workaround might be to splice into the red wire coming from the alternator and run a decent sized wire from that to the + battery terminal.

I agree. The alternator is now doing its job!   I did my road test today and on cold start the voltmeter showed better than 12.5 v. at idle.  Underway and fully warm, it holds 14v. whenever above 3K rpm, no winking idiot lights, no constantly lit idiot light.
I'm going to be optimistic and proclaim this problem is now behind me, and I look forward to a tour at month's end free of mechanical surprises.  I don't really understand what may underlay the odd behavior of the alternator, but I'm happy.
Thanks to all who offered suggestions. 
One last question.  Is there any known downside to wiring the alternator directly to the battery, as you suggest Mr. Duck?

brickrider wrote: 
Thanks to all who offered suggestions. 
One last question.  Is there any known downside to wiring the alternator directly to the battery, as you suggest Mr. Duck?

Only if you use stupidly small wire. Bigger is better, within reason. 

Bill

brickrider wrote:I agree. The alternator is now doing its job!   I did my road test today and on cold start the voltmeter showed better than 12.5 v. at idle.  Underway and fully warm, it holds 14v. whenever above 3K rpm, no winking idiot lights, no constantly lit idiot light.
I'm going to be optimistic and proclaim this problem is now behind me, and I look forward to a tour at month's end free of mechanical surprises.  I don't really understand what may underlay the odd behavior of the alternator, but I'm happy.
Thanks to all who offered suggestions. 
One last question.  Is there any known downside to wiring the alternator directly to the battery, as you suggest Mr. Duck?

I'd use at least 12AWG wire, or maybe 10.  You can buy it on Fleabay by the foot.

Check out a marine supply store like West Marine if you live near water.  They sell high quality wire that is very flexible and is tinned to prevent corrosion.