zener diode testing

1975 Commando MK III: First test: - Leads from the alternator disconnected - Engine running at 3000 RPM - Voltage across leads =~ 25 VAC Second test: - Almost new battery - Alternator leads plugged in - Engine stopped - Voltage at power outlet =~ 12.8 V Third test: - Engine at 3000 RPM -...

Went out this morning and the ammeter was showing charging of around 6 amps which is very high and I thought the Zener Diode had failed. Got home and looked for guidance on testing a Zener which all looked complicated and needing special equipment. I boiled all this info down to a simpler test...