Hello Mike,  Euro Motoelectrics sells Rick Jones book “Classic Boxer Charging”.  It’s a great little book that walks through diagnosing charging issues. Seems like most airhead owners wind up having one of these books. EME gets $30 for it, but I think it’s worth it. 

My check list...

1) Battery. As you noted, batteries may seem OK coming out of storage, but unless they were pampered over the winter then there is always the chance. My test is this: charge the battery slowly for 24 hours, remove the charger, turn ON the headlamp for 1 minute, then use a voltmeter to get a Voltage reading across the + and - terminals. This reading MUST be above 12.2 volts. If you see a reading like 11.8V or even 12.0V, then that battery is gone. An optimal battery should be 12.3V or higher. 

And as always, check the battery connections for terminal corrosion at BOTH ends of BOTH cables. I highly prefer the new, sealed, AGM batteries because they don't leak acid, which reduces corrosion issues at the battery terminals. 

2) Brushes. Replace the alternator brushes. The length of the carbon decreases over time, which in turn decreases the spring pressure against the slip rings. Poor brush spring pressure equals poor connectivity. 

3) Voltage Regulator. Replace the worn-out, 50yo, OEM mechanical voltage regulator with a modern solid state device (which has no moving parts to break or come out of adjustment). If you don't want to buy the one from Motorrad Eliktrik, then Here's One on EBay already set up for AGM's for $24.

Hope this helps.

Thanks for the info. 

Yeah...it's been on a trickle charger for days and it still only showed 11.3V so I'm sure it's pooched. I know it's been in the bike for many years so no surprise. Does anyone know a common brand battery for this bike? My local supplier does not even show this bike in their system. Thanks.

https://share.google/aimode/VJDUMPjoFTQelba2t

Looks like YTX24HJ-BS or YT19BL-BS are the most suggested sizes, and AGM to prevent acid leakage.

> There is a common battery used in lawnmowers and Harleys called the "U1". This battery measures correctly on the outside dimensions, but the terminal positions are reversed. 

> Most new batteries should be trickled for several hours before use. An AGM may require a higher charge voltage than a basic lead-acid battery to maximize their longevity. Be sure and read the small slip of paper inside the box. 

Funny, here I am back again with the same problem after installing a new voltage regulator. A buddy and I traced back to there figuring that was the problem. Now the only thing left in the system is the wiring. I have to say I have not examined the wiring between the stator and the voltage regulator so I'm thinking there lies the problem. I am heading out to start doing that after I get off hold waiting for internet support...

Back to being totally confused again. I opened it up and checked continuity from the stator to the diode board and from there to the voltage regulator. All of the wires are showing good continuity and there are no signs of any wear on any wires. New stator, new brushes, new diode board. I'm really lost trying to think where the air gap is for charging. 

We talk about an "electrical circuit". The word "circuit" means "circle". ALL electricity MUST travel in a circle and return to the point where it started. IOW, make a complete "round trip". 

Therefore, the "return path" is just as important as the wiring that delivered the electrical power to begin with. But because a lot of electrical power travels back (returns) through the engine cases and motorcycle frame we often fail to take that into account when looking for electrical problems.

Secondly, aluminum oxidizes almost immediately. Rapid oxidation is why aluminum is so hard to weld. And the only thing that makes aluminum oxidize to a greater extent is to place it in the presence of steel with an electrolyte... like say, aluminum engine cases cradled in a steel motorcycle frame, AND then adding rain or wash water !! So often times the problem is right in front of our eyes, but we "can't see the forest for the trees" !

Ohm's Law, a law of Physics (like: "Do not pass GO. Do not collect $200.") tells us that the higher the voltage the lower the issue this resistance will cause. So we don't need to worry so much about the 25,000V spark plug voltages returning to their source through the engine cases as we do the piddly 12V circuits. 

Where might this problem be ?

> Look at the rectifier board. The Airhead rectifier board gets it's return through the engine cases. Either it has 4 rubber mounts which MUST be jumpered to get past the rubber mounts, or it has 4 aluminum standoffs which may have microscopic corrosion on the threads, which impedes the return of the electrical energy the alternator is trying to produce. Because of the "circle" then, "no return" is the exact same as no (or low) energy being produced. 

> It is also possible that the recutifier board (which has 6 diodes) has issues. If one of these diodes is blown, then 1/3 of the charge current is lost.

> It is also possible that your meter is not touching the wiring where the connectors touch. 50 year old connectors must ALWAYS be considered as a problem source.... which is why I keep talking about electrical anti-corrosion compounds such as No-Ox-Id. 

> Then there is the iffy "ground" connection on the Airheads negative battery connections to the engine. A very small area of contact, brass touching aluminum (Yikes !), and a low torque on the single grounding bolt. What could possibly go wrong ?

That kind of explains why the original owner of the R60/6 I'm acquiring made this modification...

The main battery ground is no longer on the transmission breather bolt.  This bolt is critical and notorious for stripping the threads in the aluminum housing.  As the battery ground frequently gets removed for a variety of reasons, it is now on the frame under the front of the seat.  If you put it back on the breather bolt, remember to remove the spacer washer…

Ok, some good info there. And yes I am about to order Rick's book. The bike is all still apart so easy to  dig back in and have a look at your thoughts. The diode board is new and I did check them all last look.

IMHO, the steel frame is actually the wrong physical place, but the idea/thought/intent is correct.

> The major current draw is to the starter motor. So the bigger cable should be connected (optimally) directly to the starter motor. On an Airhead this is physically impossible, so the big cable can be connected to one of the 8mm bolts holding the gearbox to the rear of the engine. This cable routing ends up being hidden behind the RH carb. You may need to buy a longer, 24" automotive accessory starter motor cable to pull this off. Or, maybe you prefer to connect to one of the 6mm gearbox cover bolts on the rear of the gearbox. 

> In addition to that, I also run a 14ga Brown wire from the Battery negative post to the bonding point for the stock wiring harness. (On the R100, which I'm more familiar with, all the Brown wires of the harness terminate on the LH coil mounting plate, hidden by the fuel tank.) In this way all the low-current devices that use a Brown wire, also get a direct link to the battery. 

Think carefully about this. Connecting to the steel frame is really a terrible idea. 1) The frame has Zero electrical components in or on it. The connections to the engine and wiring harness are the priority, and the "frame" is neither of those. 2) The steel frame is a known corrosion (rust) risk. And everywhere the aluminum engine touches the steel frame is another point of corrosion risk. So you could experience corrosion putting electrical power into the frame... and then another totally separate point of corrosion getting electrical power out from the frame into the next device.

So we're working in a wet, corrosion filled environment where our biggest enemy is electrical power loss due to corrosion... and now by using the steel frame we are fighting not 1, but 2 problem areas. It's bad enough we're playing "Russian Roulette", but do we need to place 2 cartridges in the revolver ?? 

And, of course, all these points of connection need to be treated with a corrosion inhibitor, like No-Ox-Id. 

Hope this helps.

I checked the ground from the battery and the connection to the motor is good with no corrosion. Checking all of the connectors I am not seeing any corrosion anywhere and they all seem to be good. I will leave the ground attached where it is as it's doing fine right now.

I believe in Wind... which I cannot see.

I believe in Electricity... which I cannot see.

I also believe in micro-corrosion on 50 year-old connectors... which I cannot see. 

Please, do yourself a favor and start applying some No-Ox-Id anti-corrosion compound to every electrical connector (ganged or individual), relay, and "bonding point" (where an electrical cable gets bolted to something) which you have the pleasure to work on or inspect.