Odd electrical / alternator issue

[walkman]

I have two alternators, a 60a np with a ford style regulator and a new Sd-8 with the b&c regulator.

I am never reading more that about 12.5 volts with the engine running. I believe that both alternators are coming on line, the voltage doesn't drop and battery doesn't go dead with extended running. I see current in the line from the Sd-8 via ammeter and I don't see a discharge on the battery, even with the Sd-8 off. I do see a discharge with loads when it turn the alternators off. The main alt and regulator were not touched during recent panel work.

Voltage readings checked via independent means. Current also calibrated correct. I have buss voltage on field circuit at main alternator.

Stunmped.