Charging system confusion

[V12T]

My ammeter and voltmeter suddenly went hard right and I'm trying to figure out why. I've seen a previous thread but my issue seems to be different. I've watched countless videos on alt and vr testing but still non the wiser. I have two alts. On the bench with the field direct to negative I get 15-17 volts on each measured output to alt casing. Put them in the car (still field direct to negative and vr bypassed) and I get 30-40 volts at the alt measured the same way. I have left the charge wire off to avoid frying the ammeter circuit. If I connect a fused wire from alt output to battery it blows a 30 amp fuse so multimeter is correct. I bought a new vr. Across terminals was 1.7 ohms. Now it's 0.69 ohms so I've probably fried it? Two old ones I have each read 9kohms so I guess these are useless. Earths and bulkhead connectors all good. Almost battery voltage at field. Are my alternators and vrs all broken? It seems a simple circuit but clearly isn't. I'm lost!

 

[Challenger RTA]

Go through this first.

Yeah I know an other video. Check the battery.
Make sure you have the right combination.

 

[Chryco Psycho]

Propbably the VR for the guages on the rear of the dash

 

[Adam]

The dash gauge vr only puts out five or so volts to the gauges… and is not even part of the ammeter circuit iirc. This is not your problem. I believe the ammeter gets full charging circuit power.

To get 30-40 volts in the car you may have a short to ground with one of the alternator field wires. With the engine off, pull a field wire of the back of the alt and see if it has continuity to ground. It shouldn’t, but if it does your voltage regulator may sense low voltage and try to compensate. Check for a pinched wire somewhere, oh and make sure the vr body has a good ground.

 

[Challenger RTA]

This is a process of elimination. Check the battery state of charge. If you don't have the tools. Take to an auto parts store and have them check it. Alternator too. I have seen some crazy things go on with batteries.
Then check to see what the charging voltage is at the battery than at the alternator. Then also see what the voltage is at the alternator stud and batter when not running. As it could be one of the things as Adam said.
Double check engine and chassis grounds.