OK - first dumb question - how many amps is it and does it have a remote votage drop or is it all in one?
Really, all you need to do is insert the ammeter into the feed from the battery cable to the wiring harness (speaking in generalities here - don;t know what car you're planning to fit this to).
This way, the current flowing into the harness from the battery and back out of the harness/alternator to the battery runs thru the ammeter.
If it's an alternator type Landy can I suggest an ammeter is of limited utility and you'd be better off with a voltmeter? This way you're also not running all the current in your car save the starter through the bulkhead and into the passenger compartment...
Alan