low/no charging

I think your mechanic sent you down a wrong road. That procedure is for a load on the car ---such as maybe a stuck trunk lamp--that is drawing an unwanted load when car is not running/ parked

First thing.......determine what you have for a charging system, that is, do you have the original system?

Your original "type" alternator should only have two wires........the big battery output stud, and the smaller "push on" field wire.

You MAY have more than one problem...........You said

"Directly on the alternator It measures 0.08V"

If you are talking about from the output stud to ground, there is no continuity from there to the battery. That output stud feeds IN through the bulkhead connector, TO AND THROUGH the ammeter, and along the way branches off to feed the fuse panel and ignition switch..

AFTER going through the AMMETER, it comes back out the bulkhead connector (now red) and goes through the fuse link, and attaches to the STARTER RELAY, the large battery stud

A quick check is to remove the field wire, and use a clip lead to jumper from that terminal to the battery. This should cause "full output" from the alternator at a fast idle.

If not, recheck battery voltage, and the voltage on the alternator output stud.

If, under the above conditions,
If the alternator stud is quite high, above 16V, and the battery is still low, below 13.5, you have a wiring problem from the alternator, through the bulkhead, and back to the battery

If the alternator and battery are still quite low, below 13.5, the alternator is not charging

If the alternator and battery are above 13.5, it should be charging, and should indicate on the ammeter, if it is still functional.

If this last is the case, you either have a wiring problem in the regulator / field circuit, or the regulator.

To check this out, hook the field wire back up.

Disconnect the regulator and jumper across the two wires. This should cause a "full output" condition as the first part of the test.

If doing so causes the system to charge,

First remove and scrape the regulator mount clean, remount and be sure regulator is grounded,

If the above does not cause system to operate, replace the regulator.