2002 Moomba Outback V
310 Indmar TBI

I replaced my alternator because I kept draining getting low voltage. I installed the new alternator and it still is putting out 11.8 volts. I have tested both batteries and they are fine. I noticed that the purple and red wire that plug into the regulator on the back on the alternator shows 12volts before I turn on the ignition, but when I turn the ignition to the on position the voltage drops to nothing. I am not sure if this is wrong or not but if it is what could be the culprit and what should i check??

any advise helps

thank you.