Alt. guage discharging all the time???

had same problem with mine. After doing everything you did, I straight wired the amp meter ammeter?? through the firewall connection. Took my dremel and drilled a hole where the two ammeter wires went through firewall connection. Ran new wire straight through firewall and spliced into old wires with connectors. Problem solved. Just ended up being a bad connection at firewall.
Like I said, did everything you did- replaced alt, volt reg, put in extra grounds, new battery, etc etc. "Bypassed" firewall connectors and now everything works. By taking out old connectors at bulk connection and drilling through plastic, looks somewhat original and clean. Took about an hour of taking my time.