Alternat approach to Higher Amp Alternator

[Bullitt-]

                 Anyone with any electronics experience please chime in.

I Googled up some info that has me thinking about trying an alternate approach to wiring in the later model high amp alternator.  I know I have to provide a larger wire to connect directly to the battery but I would like to keep my ammeter working. Seems that if a shunt(resistor) were to be placed in the circuit in parallel with the existing wiring some function of the voltmeter would be retained... My problem is what size shunt would it take to re-direct about 15-amps(staying low to be on the safe side) through the existing wiring.

There are several articles on the subject, all say about the same thing...here is one.
http://www.allaboutcircuits.com/vol_1/chpt_8/4.html
 

[Chryco Psycho]

On a customers car I ran 2 10 Ga wires , 1 to the existing harness & one to the battery directly , his ammeter still moves just not as much