Chris T wrote: I have wondered whether current from the alternator goes through the whole of the main circuit as well as the battery, but your statement suggests not - that it goes to the battery and the current from the main circuit is generated from the battery. If the battery is topped off ie fully charged -as mine is - brand new and most times hooked up to an intelligent charger - then it reads zero. Therefore when the bike is started and the coils are taking electricity to create sparks, and a light is on, then presumably it is normal for the ammeter to show a drop in available current - ie to hit negative - as some of the current is being used. But if so, then would not the battery put out more current to compensate and bring it back to zero, and if the battery is fully charged would not some of the current that is going to the battery from the alternator effectively be utilised to bring the main circuit back to zero or into positive? That should bring the amperage in the main circuit back to zero almost instantly?

It looks like the voltage vs. amps as been explained pretty well. I like Dave's analogy of a hose under pressure (volts), and flow (amps). Unlike the water going onto your flowerbed though, the water has to go back to the sump for the pump, (battery and alt), to pick it up because its a closed system.

The battery and the alternator/rectifier-zener, are wired together like each side of a Y. The tail goes to the hot post on the ignition switch. The battery has about 13V and the output of the alternator is variable between zero and around 14V. If you turn on the ignition and hit the lights without starting the engine then all the power is coming from the battery and the ammeter needle moves to the left. When you start the engine and begin to spin up the alternator, it's voltage starts to climb and it's contribution increases and the needle moves closer to the center. When the output of the alternator matches the 13V of the battery, the needle is centered. When it goes over 13V then the pressure is higher than the voltage of the battery and the flow could reverse into the battery. But the thing about rechargeable batteries is that they will only charge to a certain capacity and that's all. If your battery is new and you keep it on a tender then it's full, and if the extent of discharge amounts to the time it takes for you to turn the key and kick it over and ride off then you're probably never going to see the needle move to the right very much at all.

You mentioned that the Sparz cured the problem, does that mean it stopped missing and stalling? What the charge on the battery when you get home? You do have the ammeter hooked up to the wire between the battery and the ignition switch, right? Not hooked up to the alternator like an assimilator? When people do that the ammeter usually has a life expectancy of about half an hour.

You mentioned that the Sparz cured the problem, does that mean it stopped missing and stalling? What the charge on the battery when you get home? You do have the ammeter hooked up to the wire between the battery and the ignition switch, right? Not hooked up to the alternator like an assimilator? When people do that the ammeter usually has a life expectancy of about half an hour.

Bob, after rereading my original post I realised that I had not made it clear that the missing and stalling only (apart from one instance) occurred when I had been riding with the headlight on. After an hour or so if I came back to town and stopped in traffic it would stall, which I assume was because the battery was drained. The one occasion when it happened without lights on was when the bike had been stored and not ridden for some time, and I assume that I had allowed the battery to run down, and it did not fully recharge before I rode again.

No the ammeter is not hooked up direct to the alternator; the alternator and regulator goes direct to the battery, and the main loom comes off the battery - completely standard 1970 loom.

I didn't actually test the voltage on the battery after the last ride; the bike is at our beach place for the summer, and I did all of the testing down there with an auto electrician, because I didn't trust myself to do it properly and wanted to have some independent verification in case it did turn out to be a fault with the regulator; and I forgot to take my own voltmeter down there; I am hoping to ride again this weekend and will test it then.

Thank you for everyone's input. I think that I will attempt to test the resistance through the ammeter this weekend; I assume that I can do that by putting a voltmeter over it - set to amps? - and getting a reading as to the amount of current? I had a look at a video on facebook about testing regulators, and assume that the same process would work for testing the ammeter?

The ammeter on my Norton has always been erratic and reading from the neutral to minus amps and scaring everybody that rode it but not me! I figured out a long time ago that when I start it and turn on the headlight in the garage and rev it a little...... the lights get brighter removing all doubt about the ammeter and charging system. It's the nature of the beast.
Recently we bought an accurate kit Cobra with english instruments and the ammeter would not show a charge. After replacing inspecting and fiddling with the electrical system I realized that it was the same instrument as the 69 commando has and will never show a charge for whatever reason. Lucas, Prince of darkness