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The Yahoo picture is poorly drawn. The brown wire from the ignition switch going towards the coil can't be connected to the wire on terminal 2 of the voltage regulator else the ignition key would not stop the engine. That terminal 2 on a four terminal alternator regulator is odd. Probably peculiar to Lucas as on a British made MF tractor. The right way on the other link is good. The only thing connected to the battery and not through the ammeter is the starter. All loads and charging goes through the ammeter. Large well insulated wire is an asset. I had an 8N with an ammeter that had no terminals. The wire just passed through a clip and the magnetic field from the wire move a magnet attached to the pointer. The same thing happens in the automotive ammeter, just that single wire is inside and there are terminals. If one is going to futz about under the dash with wrenches and get close to the ammeter terminals, one should disconnect the battery ground connection FIRST. Or cover the ammeter terminals. As well as those for lights and the ignition switch. As for usefullness, the ammeter wins in my opinion as stated before. The voltmeter is fully capable of giving misinformation or just no information from lack of resolution. What are the failures of the charging system? Most common is a corroded battery connection. If it comes loose while running, the voltmeter will happily indicate full charge the instant the engine is running, but the battery isn't taking charge. The voltmeter might go to zero when trying to crank though. The ammeter will show zero when turning on the ignition or lights or charging in that case. With the bad connection, the ammeter will show reduced current for lights and ignition loads (though the dim lights should be a hint of dead battery or bad connections). The ammeter shows a peak of charge right after starting which tapers off as time goes by with a constant voltage comming from the voltage regulated generator or alternator. If the voltage is correct or low the current will taper to zero. If the voltage from the charging dynamo is high the current won't taper to zero and the battery will need water often. When the battery gets old and sulfated the current won't drop with time but the voltage goes to the charging voltage and stays there. So the ammeter shows the lack of charge taper but the voltmeter shows full charge. All voltmeter readings are more useless when they aren't at the battery terminals. The voltage under load or charge anywhere else in the wiring is different, low for loads, high for charging. And so is again misleading. Back about 1965 I mounted laboratory quality voltmeter and ammeter (with remote shunt) in my VW bug on a six volt system. The voltmeter just didn't tell me nearly as much as the ammeter. The ammeter showed me the failings of the electromechanical voltage regulator with relay cutout and when I stuffed a newer engine with a 12 volt generator (generators not interchangeable) I built a solid state voltage regulator with diode cutout that was significantly better for battery life because it stopped the ten amp reverse current typical of the cutout when running too slow to charge but too fast to get the cutout to open. Which seemed to be at common city driving speeds. I tried testing my 4020 generator charging with a voltmeter. I learned nothing using a Simpson 260. It hinted it was charging but I kept having to put a charger on to get enough into the battery for starting. Yes voltage rose, when charging but not enough. I mounted and wire an ammeter. It bounced from peg to peg even after I put in new brushes and polished the commutator. So I mounted a 10-SI alternator. Now the battery charges in ten or 15 minutes of running and I've not had to charge the battery with the AC charger since. Originality is nice but there's no provisions for hand cranking the 340 cubic inch engine. I don't think I'd try if there was! Gerald J.
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