According to the guy at Powermaster when I asked him about Ammeter accuracy, he explained that the same current is going down both paths so there will be no difference in ammeter accuracy. The current is not split evenly because more current is needed down the accessory line than the battery.
The shunt does bypass the ammeter, but all of the current of a 150 amp alt would go through that one path where all of your accessories are connected. It made sense to me to add a second wire. Also, if a big honkin fuse holder is a problem, a fusible link is more fashionable (as in undetectable if covered just like wire). Don't put it at the battery end though. Battery gasses could be ignited if that link ever blew.
He wasnt a fan of the vintage full current flow ammeter and really encouraged me to change over to a voltmeter. It's like I said Carl, you should contact Powermaster to confirm. I put things out there and try to be as accurate as I can, but nothing like talking to a real expert.
