Wondering which wire to use to wire in an ammeter. Does 65/0.30 sound right?
My advice would be to stick with a voltmeter, far to much to go wrong with an ammeter circuit even with a huge fuse in line..
Certainly make sure the ammeter has a big enough capacity and that the cable you use has at least 10amps more capacity that your alternator output. Also make sure you crimp and solder connections and use some very good grommets through the bulkhead to avoid chaffing.
I think you are much safer with a voltmeter, a voltmeter actually shows more information than the ammeter, and is also safer to wire in since it takes no current and this allows the use of a small (1A or less) fuse. It indicates whether the battery is being charged. A reading of ~12V indicates that there is no current flowing into or out of the battery. Less than 12V indicates discharge (typically 8V when cranking the starter) and 13-14V is a healthy charging voltage. More than 15V when charging indicates a faulty regulator on the alternator. Charging at too high a voltage may significantly shorten the life of the battery.
An ammeter needs to take the full normal load. This is 30A or so for a Seven, but add a few extra lights etc and it could be much more. This means that in the case of a fault, the wiring will be at risk of melting if the fuse does not blow quickly. Depending on the fault, a current of 50A -100A might flow for a few seconds, enough to start a fire or cause a serious burn.
Just my 2 pennies.
I agree with Phil....nearly caught fire to a modded Mini a few years back when the wiring melted behind the dash-board.
Got a Amp Guage on the dash but only have the Volt Metre wired up. ::)