Cool discussion, I plan on running both when I upgrade to a 12v alt from a 6v gen.
On my 49 the brake light switch wiring can come loose from the switch. They are barrel type connectors that slide on and pinch to two posts on the switch, most of you know this. In any case, the connections sometimes work loose and I loose my brake lights.
The ammeter tells me when this occurs when sitting at idle at a stop. It will show a slight neg deflection with the brakes applied. As I let off the brakes the ammeter will either deflect back to "0" or show a slight pos deflection. I use this to determine if my brake lights are functioning properly.
It's also good when driving at night with the lights on. In this case I know when to bump the idle up enough to either zero out the ammeter or increase rpm more to show a charge when idling at a long stop.
I like a voltmeter as it tells me the basic condition, i.e. charge on the battery with the key ON but no other load applied. Then once started it'll tell me the basic condition of my charging system by indicating how much voltage over the key on voltage reading the charging system is putting out.
Both can and are very useful indicators, especially for those who like indicators
Dave
