You may have multiple problems. I'm on an "alternate computer" and have connection problems
The alternator may not be outputting it's full potential due to a problem (bad diode, etc)
The alternator may not be large enough capacity
The charge wire may not be large enough or have voltage drop on the way to the battery
Start by comparing your battery voltage to the voltage at the output stud of the alternator. Easy way to do this is once again, the "voltage drop" method. Just put one probe on the battery positive, the other probe on the output stud, and turn on "stuff" to heavily load the charging system. Depending on how large the wire is form alternator to battery, I would not expect to read OVER 1/2 volt, the LESS the better
If that's OK, check FOR SURE the belt is good and tight and not slipping
Then alternately monitor three things under heavy load
1 Make sure you are getting good battery voltage to the blue field connection of the alternator
2 Unhook the green field wire and clip that exposed alternator field terminal to ground Monitor that under heavy charge, the blue field is "close to" same as battery IE so that you are getting full field current
3 Load the system, fans, lights, etc, and see if it keeps up. If not, and if the voltage drop from the alternator output stud tot he battery is not excessive, you simply either don't have a large enough alternator, or the one you have has a problem
