In the dash board?

Depends if you want to measure current draw or charge rate...if it's charge rate then it needs to be inline on the alternator cable and will have to be able to measure up to about 120 amps...

If you want to measure current draw then you could either have the ignition feed running through it or the 3 fused links at the battery. You must NOT run starting current through it though or it will be a molten mess stuck to your dash....

I personnaly would only use the ammeter to measure charging amps then you know when the alternator is charging. It would be more useful than current draw as you won't know there is a problem until you end up on the hard shoulder. If you want to know if your alternator is up to the job and can supply enough amps to cover all the electrics then just check it with an inductive clamp meter with everything switched on. I have an inductive clamp meter if you want it checking...

It also makes me wonder how many cossies out there have had an alternator refurbed and have ended up with a 60 amp regulator in it instead of the standard 90. I have seen this a few times....