Richard/SIA,
I have seen the shunt circuits talked about but have never played with a automotive one. From my limited experience with industrial types I would think you would need a new ammeter calibrated to the values of the shunt. I don't think you can just stick something in the charging circuit and expect the existing gauge to read correctly.
I know this wasn't the point of your original question, but I'm sure you know a voltmeter could tag into the system without having to pass all that current and with a little understanding, you can read it just as well as a ammeter.
This would of course mean you would have to disable your existing ammeter by kicking it out of the circuit.
Keep us posted if you find out the secret of adapting a shunt to the ammeter you already have in your rig.
Stuart
