[DML] Electrical problem

[ToniLFHS98@xxxx]

To all:
I need help to diagnose the problem with the charging circuit on my 81 D. My 
ignition light stays on and my voltage meter indicated 11 volts and dropping. 
Since I have the original Ducellier alternator, I automatically assume that 
the alternator has gone bad and promptly ordered a replacement from PJ Grady. 
This morning after I replaced the alternator, the same problem remains. Now 
I am at a lost as to what's wrong.
The problem with the ignition light started shortly after I have the A/C 
recharged with 2.5lbs of R-12 and now the A/C works beautifully. Could it be 
a defective replacement alternator?
Thanks in advance for any info that can help solve the problem.
Bill