Wiring upgrades and ammeter operation

Well you don't disconnect it. Read the MAD article. This is an excellent way to go with minimal changes to the car. There's a thread "on here" about converting various clusters to a voltmenter

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

http://www.forabodiesonly.com/mopar/showthread.php?t=119480&highlight=ammeter+conversion

The main problems with original systems is.........

1....The bulkhead connector terminals were never designed to withstand the amperage, even 30A. These same basice 1/4" spade connectors are used in electric furnaces, and even at the nominal 20A of a typical furnace element, they do fail

2....The factory wiring, really was undersized, especially in earlier cars

3....The ammeter, depending on car model, is a poor design and poorly made. The ammeter itself can and does fail in a few different ways

4...."Ma" "herself" knew this........this is why so called "fleet wiring" exists. This is documented in some service manuals as the optional 60A alternator wiring. The ammeter wires were larger gauge, and were run through the bulkhead using separate grommets. The original RED ammeter wire was abandoned. Leads me to believe many (all?) of these were dealer installed.