Amp Meter issues

What you've experienced is IN PART (and only in part) of why there has been so much written about the ammeter circuit. There is more to it (many times) than just the ammeter. In general, the possible problems are:
1....Many times aggravated by the installation of a much larger alternator, and or addition of large load accessories

The usual suspects are the bulkhead connector terminals, the welded splice (rare) up under the dash, the ammeter wire terminal ends, and problems in the ammeter itself. What happens there is that there is really nothing for the nuts to actually tighten against, and in newer cars (my old 70RR) the cluster housing is PLASTIC. Head causes things to loosen, the looseness caused more heat, and pretty soon you have actual smoke and heat, not to mention sparks and worse.

I would NOT simply bolt those together and go on your way. Pull the bulkhead connector apart, at least and inspect the terminals. And read the MADD article on the subject:

http://madelectrical.com/electricaltech/amp-gauges.shtml
Many of us here agree that there is an easier way to do the bypass rather than in the article

AFTER you have inspected and fixed problems in the bulkhead connector, and inspected and bolted the ammeter wires, now take some nice big wire, like maybe no8 or no6 AND A BREAKER OR FUSE and wire from the alternator output stud direct to the battery, starter post, or starter relay "big stud."