Ammeter Maxed

A few things about the alternator voltage dropping

1..First forget the ammeter reading. As I told you earlier you have the fans and possibly other loads wired "on the wrong side" of the ammeter
2...It may be that you have serious voltage drop in the "ignition run" circuit which feeds both the alternator field and the VR. When this drop is not too much, it actually causes OVER voltage. But you may have a more serious drop, OR you may have added stuff to that circuit causing the same problem.

3...The other thing that can cause this, or it could be a combo of 2 and 3, is that the alternator simply is too small to output enough amperage to keep things "up." Add up pumps, fans, whatever is running, AND if the battery is somewhat low. it may be the alternator is too small OR THE alternator may have something wrong with it such as a bad diode that partially reduces the output OR THE alternator may have been mis-labled and is not the output rating you believe it to be

4...To find out if the alternator is large enough and is working at that rating, disconnect both field wires from the alternator. Get some no14 wire and appropriate connectors and "rig" the field to ground either field terminal and wire the other field direct to the battery with a GOOD connection. Do not power this until you are ready to test.

Now monitor battery voltage and also get in your mind to also check the alternator output stud, those two points. Get the car running, hook up your field "rig" and monitor battery voltage and modulate engine RPM to keep voltage below 16. With EVERYTHING running and with the engine running to simulate "low to medium cruise" RPM check that battery voltage is up to at least 13.2 or higher. IF NOT check the alternator stud and see if that reading is a lot higher. If it is more than 1 or 2 V difference, you have a SERIOUS drop problem in the wiring between alternator and battery---that being the bulkhead connector, the ammeter, and so on

5...If the above checks out OK, now wire up everything "normal" except "rig" the branch at the ballast (or where it was) so you can jumper direct battery power into that circuit. This will eliminate voltage drop from the ignition "run" circuit. Jumper power into that from the battery and again see by battery V if the system will keep up. If (4) checked out OK and test (5) checks out OK you likely have a serious voltage drop from battery--through bulkhead--through ignition switch--back out through bulkhead--and to the IGN1 "run" circuit feeding the field and the VR IGN terminal.