Here's how I bypass the Ammeter without ripping the dash apart.
From the Battery stud back of alternator run a wire to the Battery stud of Starter relay using a fusible link at the relay.
I use 10 gauge wire with a 14 gauge fusible link.
Done.
Takes 50% load away from the ammeter gauge and if ever the gauge craps out you can still drive the car. Bonus is should the fields in the alternator reverse polarity,the fusible link will pop and not melt down the dash and wiring of car.
Optional is adding a voltmeter simply using a switch 12 volt source and ground anywhere to t he dash or whatever.