This might mean the ground is isolated from the case of the alternator. In a normal application, the case of the alternator is the ground connection and being bolted to the engine block via a metal bracket, the grounded case of the alternator is electrically connected to the ground lead of the battery which is also connected to the engine block. An isolated ground might indicate the alternator ground is electrically insulated from the alternator case.
Possibly the voltage regulator has a poor ground or poor +12v?
with a voltmeter
The 1960 Thunderbird was 12 volt negative ground. The 1955 Thunderbird was 6 volt positive ground and 1956 and up was 12 volt negative ground.
Check fuseable link on alternator Check fuseable link on alternator
Purchase a power inverter.
If the light stays on it indicates your charging system has malfunctioned. Usually this means the alternator has failed, but not always.
Use a digital volt meter set to the 20 volt DC scale. A good alternator will output 13.5 to 15.5 volts.
I hope not, it'll cook the 12 volt DC system.
If we are talking about cars only: the system that charges the 500 volt battery in a Hybrid is a Alternator. So in theory there is no limit. Most cars are "12 volt" (common usage, incorrect) systems.
13.5-14.4
Check the ground connections. Can also be defective battery cables. Check all cable connections on the + & - cables. Also check the alternator drive belt.
Yes. It is done all the time in automotive electrical systems. The alternator, which creates AC, has its current rectified using diodes.