(quoted from post at 18:21:14 03/08/13) They both have their uses. Ammeter tells you whether you're charging or discharging, voltmeter tells you how much voltage your battery is putting out. Of course, if your voltmeter reads low, obviously you're not charging.
An ammeter will be more useful with a 6 volt system due to the limited availability of the smaller scale volt meters. Most volt meters are ranged for 12 volt systems.
Detroit moved away from ammeters due to the potential fire hazard they posed behind the dash. Volt meters are safer and carry less liability.
My personal choice would be an ammeter because it tells you immediately when you're charging system is acting up - With the large amp hour capacity of modern batteries, there will be a delay in registering a problem with a volt meter.
Now let's talk about converting to electronic ignition.......... ;-]
1) "Ammeter tells you whether you're charging...."
You can show amps but still have a low charge...
You are 0 for 1
2)"voltmeter tells you how much voltage your battery is putting out."
The battery is a place to store power a voltmeter will show you the state of charge of the battery and the charging system...
You are 0 for 2
3)"if your voltmeter reads low, obviously you're not charging."
You are 1 for 3
4) "An ammeter will be more useful with a 6 volt system due to the limited availability of the smaller scale volt meters. Most volt meters are ranged for 12 volt systems."
2 for 4
6) "Detroit moved away from ammeters due to the potential fire hazard they posed behind the dash. Volt meters are safer and carry less liability."
If you say so thats worth a haft point
You are 2 1/2 for 5
6) "My personal choice would be an ammeter because it tells you immediately when you're charging system is acting up"
That's not a completely true statement it depends on the state of charge of the battery and the demand of the electrical system...A voltmeter does the same thing but will tell you more about the state of charge of the battery and gen/alt output...
You are 2 1/2 for 6...
Theirs also a chance and it happens often were a voltmeter are a ammeter will show a low charging state... Sometimes a battery will not accept a charge the regulator is satisfied so you have a low voltage/amp output but suffer from a slow no crank condition from the battery and starter... This is reverse of what folks would think and the hardest condition to diagnosis...
I have also had battery's that would not fail a load test and never show signs of failer... The complaint was low volt/amp output with the gauge are the charging light on...
Its like a compression test the test leads you to your next move I could not imagine trying to diagnosis a charging/starting system using a amp meter only are using a amp meter as my fist weapon... Like a compression test a voltmeter leads me in the direction I need to go its valuable info I must have... Are I will chase my tail waist my time and the customers money and not make a wild guess like you normally see... To bad voltage questions were not on the guru test...
This information is provided for those that want to strengthen their diagnostic ability,,, YMMV...
Ammeters vs. Voltmeters
Ammeters and voltmeters are the opposite of each other not only in terms of construction, but of circuit placement.
Ammeters must have current passing through them in order to measure it, and so must be placed in series inside of a circuit. Polarity must be observed, and their positive and negative leads must be connected to the positive and negative sides of the circuit, respectively. Also, their internal resistance must not be large or it will block too much current, and this will affect the way the circuit functions and hence the reading.
Voltmeters should not have any current passing through them, and so are placed in parallel with the circuit they are to measure. Their leads are placed on each side of the component of interest, and as with ammeters, polarity must be observed. If their internal resistance is too small it will not block enough current, and this will affect the measurement.
Ammeters vs. Voltmeters
Ammeters and voltmeters are the opposite of each other not only in terms of construction, but of circuit placement.
Ammeters must have current passing through them in order to measure it, and so must be placed in series inside of a circuit. Polarity must be observed, and their positive and negative leads must be connected to the positive and negative sides of the circuit, respectively. Also, their internal resistance must not be large or it will block too much current, and this will affect the way the circuit functions and hence the reading.
Voltmeters should not have any current passing through them, and so are placed in parallel with the circuit they are to measure. Their leads are placed on each side of the component of interest, and as with ammeters, polarity must be observed. If their internal resistance is too small it will not block enough current, and this will affect the measurement.
Ampmeters must have current passing though them in order for them to measure it (not of much help on a no crank)
http://www.egauges.com/ATM_Tips.asp?TipPage=voltmeterammeter.htm