Super A not charging battery

My 48 Super A was switched over to 12V by a PO and operated fine until last year. The chevy alternator quit working, and I was relying on the battery charger to keep the battery up. I replaced the alternator and had the battery checked (ok). As far as I can tell, the alternator is not charging the battery. There is a button on the dash, the PO called it an "excitor"? that you had to push, then the amp gauge would jump to positive charge. Since the alternator has been replaced, puching the button actually causes the needle to go negative. I know I replaced the wires exactly as tey were before. What should I be checking next? Where can I check the the voltage safely?

Todd - Your last question 1st:

Check the voltage between the large BAT terminal on the alternator and the alternator case -OR- directly across the battery posts.

With the engine running you should see 14.0 - 14.5 volts. 12.6 volts or less says the system is not charging.

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Regarding the "no charge" problem try this first:

Run the engine up to max RPM then push the "excite" button. It may simply be the replacement alternator has a higher "turn on" RPM than the old one.

If that doesn't work pull the aux connector from the alterator then test each connector terminal for voltage. You should see battery voltage at #1 when the "excite" button is pressed. And #2 should show battery voltage at all times.

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If the above checks out (indicating the wiring is OK...) the problem could be the replacement alternator has problems. You can isolate the problem with this test:

With the engine running at about 1/2 throttle push the "excite" button. Now take a small screwdriver and touch its tip to the tab inside the D-shaped opening on the back of the alternator (photo). While keeping the tip in contact with the tap ground the screwdriver shank to the side of the opening.

If the ammeter show 20+ amps charge with the tab grounded it means the alternator's internal regulator is bad. However if still no charge the alternator is NG. Note: You can replace the internal regulator yourself for around $10.

Good luck!