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As the upgrade on the "78 R100 continues, my problem with the charging system has me completely mystified. I have replaced the regulator, alternator and diode board THREE times completely, swapping and testing parts individually. Continuity tested all the wiring, cleaned all the connections, swapped out the battery and gone back over it again and again. The instruments were smashed some years back, so I kept the remains of the printed circuit and bulb holder, as this is an integral part of the system, and mounted them in a custom made housing. Up until a few months back, this was no problem. All of a sudden, the charging light stays on at all revs, the battery goes flat after a few days, and I now resort to putting it on the charger over night, every night, as it is my primary transport to and from work.

I cannot for the life of me figure out what it could possibly be, and I live in a fairly Isolated area with no prospect of getting any help from someone who knows about '70's BM's. I do my own work anyway, except for specialist machining etc, and thought what I had was a fairly reasonably handle on electrics. All I'm doing is wearing out my multimeter looking for a gremlin The only possible thing I can think of is the charge warning light is the culprit, so if any one has even a distant hint of an idea what to check for it would be greatly appreciated. Next step is to cut into the wiring harness, isolate the charge warning light wires, and make a complete new custom circuit and bulb holder. The bike is very high mileage, and I 've just spent $4,000.00 totally rebuilding the top end, gearbox and side car running gear, so I'm not about to give up on a wiring hassle As Sherlock Holmes reputedly said, once you have discounted everything else, what you have left, no matter how improbable, is the answer....

What's the status of the rotor...you didn't mention that? As for the charging bulb and functionality, Snowbum has a workaround on his website to install a resistor at a specific spot in the circuit to keep the system working if the bulb should burn out. Might be worth doing that to eliminate the bulb/circuitry as a problem.

Kurt in S.A.

What is the voltage on the battery at 3000 RPM? You said alternator was replaced, but which part? Short brushes may keep the system from charging, but this should cut off the charging light. Check resistance of the rotor by measuring between the slip rings with the brushes isolated. The three phase AC from the charging system can be measured prior to the diode board and while I do not know exact values should easily exceed 14 volts.
Bob

When these things happen to me, I nearly always find that something that I "assumed" turns out to be the culprit. I might not have consciously assumed it, but none the less, I discounted it.

Snowbum's resister mod is a good one.

Solved it!!!!!!! Turns out it was the bulb holder circuit after all I replaced the whole sysytem with one from a working bike, and the warning light still stayed on . Nothing left to check anymore, as all the previous components had been tested thoroughly, and it could only possibly be the bulb circuit. I pulled the bulb holder completely apart, removed the pins that plug into the wiring harness, and soldered 14 G silicon wires to the pins. I then soldered the other ends onto the bulb holder, and rechecked. So far so good.......after reading Snowbums article on soldering a resistor into the circuit, I took the plunge and did just that, although I had to solder two resistors in series, as I did not have one that was 320 ohms. Plugged the two pins into the corresponding female connections in the Instument housing connecting plug, and switched her on. The light came on, so I started her up, and the light went out at idle I increased revs, and the voltmeter shower a steady and progressive rise in voltage at the battery, then switched her off and on again. The light came back on, and I retested with the same results. Looks like I'm back in business.

Thanks for the input everyone, but special thans to my teenage son who was home from Uni for the mid year break. He's studying Engineering and has a good head for electronics, so it was great to have him here to help out with diagnostics and his supply of resistors and connections. I now have 3 complete working charging systems as spares, and after all that work, I feel confident in helping some one else out with charging gremlins. Alls well that ends well

The German's seemed to use the bulb to use for the exciting current to establish the field in the alternator for charging. My old VW diesel pickup was the same way. Glad you got it figured out!!

Surely feels good, doesn't it? With your tenacity you will have more triumphs.

Duane Ausherman wrote: With your tenacity you will have more triumphs.

Who's bloody side are you on!?

British bikes are a case of blind perseverance in the face of staggering reality. But the wiring is the least of a Triumphs problems

Duane Ausherman wrote:Surely feels good, doesn't it? With your tenacity you will have more triumphs.

Are you referring to me??