[pontiacmonstr]

whats the difference and which one is best to use in your old car?

[LeighP]

Amp gauge requires you to run the main current supply through the gauge....I don't know any auto electrician who recommends still using them. Volt gauges are more useful anyway, lets you know the system voltage rather than just the current draw at the moment.

[chrisinestes]

Think of it in relation to water... Volts would be the water pressure in a pipe... Amps would be how much water is flowing in the pipe.

[chrisinestes]

An amp gauge actually uses a shunt... a type of very accurate resistor. A certain current through the shunt creates a certain voltage across the shunt, which is shown on the guage. With a shunt, the full current doesn't have to flow through the guage.

[Half-Inch Stud]

I'd figure on a Volt meter so I can see 14.4V vs 13.8 & less, to indicate alternator health.

Not always easy to know the alternator is working without that.

[stellar]

Use both-- best of both worlds

[Stuckinda60s]

Simply put, a voltmeter can be hooked up anywhere in the system, across the battery. You can hook the positive to any switched/fused connection and the negative to any good ground point. An ammeter needs to be hooked in series with the battery flow so it requires all the current to flow through it. Hooking a voltmeter up that way will fry it because it has no shunt across the meter movement.

A voltmeter can give a good indication of potential problems by watching the meter when starting, if it falls below about 10-volts, that's an indication you may have problems developing. It also shows charging system problems as they develop. Battery voltage will drop even though an ammeter might indicate that everything's okay.

[wrenchmen]

As stated above, not all Amp Meters need to have the current flow through the actual amp gauge, some styles have a remote mounted Shunt and only smaller gauge wires are required to run to the actual amp gauge.

here is an example....http://www.cruzpro.co.nz/a60.html

I would just keep it simple and use the volt gauge.

[george kujanski]

The traditional aftermarket ammeter requires that the main cuurent path be routed thru the firewall, thru the gauge, and back underhood.

The large body Pontiacs had a shunt as part of the underhood harness which required only two smaller gauge wires to be run to the internal gauge.

A voltmeter is preferable to use as part of a gauge package, but being who I am, having both would be cool, but I wouldn't use the traditional aftermarket style.

George

[Old Goat 67]

Having the

traditional aftermarket ammeter requires that the main current path be routed thru the firewall

, can be hazardous to your sanity when you accidentally ground one of those lugs while fooling around under the dash!

[Steve Barcak]

Originally Posted by Stuckinda60s

Simply put, a voltmeter can be hooked up anywhere in the system, across the battery. You can hook the positive to any switched/fused connection and the negative to any good ground point. An ammeter needs to be hooked in series with the battery flow so it requires all the current to flow through it. Hooking a voltmeter up that way will fry it because it has no shunt across the meter movement.

A voltmeter can give a good indication of potential problems by watching the meter when starting, if it falls below about 10-volts, that's an indication you may have problems developing. It also shows charging system problems as they develop. Battery voltage will drop even though an ammeter might indicate that everything's okay.

Several good answers here. I like this one the best. A volt meter is one of best guages to have on your car. Pontiac did not really run these until the '70 Firebirds, GTOs in '73.
They are easy to hook up and are a great diognostic tool ( as is a fuel pressure gauge).

I have both on my '66 GTO and highly suggest everyone doing the same.