This is a picture of an ammeter installed in a customer's Gold Wing. I am a huge fan of ammeters on motorcycles. I believe the last one put in by a factory stock, on a motorcycle, was on Kawasaki's Z1R. But they were once quite popular. And I believe for good reasons.
The ammeter is a compensation monitor. If at any point the meter reads a loss without showing an immediate compensation, there is something wrong with the electrical system. Engine rpm, the battery's charge state, and vehicle electrical load all influence the ammeter's reading. Thus the needle normally moves around all the time as the engine is throttled and you change gears.
As the bike is ridden, the back-and-forth swing of the needle will gradually decrease, until after some time the swing from low amps to high amps will be small, in fact minimal, indicating that the load pulling on the battery is equal to the push coming out of the battery due to the bike through riding having refreshened the battery's charge. At its least active point the ammeter's needle will hover almost but not quite motionless around a point on the meter slightly above 0, say between 0 and 1. I.e., half an amp. However, at a stop light the needle will again dip below 0, and accelerating from the light, the needle will swing an equal amount above 0, and as the vehicle moves this swing will repeat, gradually lessening, i.e. narrowing, until again it is minimal, quivering around the slightly above 0 point again. So, widest with little positive charge on the battery, narrower as the battery is recharged. But always swinging back and forth, even if just perceptibly, and always centered slightly above 0.
This is a scenario that many find unintuitive, even difficult to understand, and it is probably why ammeters fell out of favor some years ago. The way to think of it is when in science class in school the teacher moved a magnet near a piece of wire tied to a -- guess what, an ammeter! Each time the teacher moved the magnet left, the ammeter's needle moved one way, and each time the teacher moved the magnet right the ammeter needle moved in the oppostie direction. This same thing happens on your bike. Once you have spent some time observing it, you will intuitively find the ammeter faithfully represents the interplay between battery and alternator, offering a moment-by-moment picture of the health of the charging system. You will probably be surprised that the battery loses so much charge upon starting the vehicle, and equally amazed that the bike replenishes that lost energy so quickly as it is ridden. Each load, as it is introduced and then removed, will display on the meter. The turnsignals, for example, will cause the ammeter needle to wiggle in time with the flashes. The brake light will show as a slight dip of the ammeter's needle. And as already mentioned, the starter's maximum downward dip will be compensated for with an equally strong upward swing. The lower the ammeter needle's dip downward, the higher its resulting swing upward again. Consequently, very small dips are followed by very small upward compensations.
I believe this offers a more realistic picture of battery and charging system health than does a voltmeter. Ammeters are actually more available today than they have been in decades thanks to the huge vintage parts industry. Though a little tricky to install, it is well worth it.