make sure the ground reference is present. Usually there is a battery lamp on the gauge cluster that completes that circuit. If that lamp burns out the alternator will not charge. You can verify by turning the ignition on and seeing that the battery lamp illuminates and it will go off when the alternator is putting out power.
also make sure the alternator pulley is not slipping on the shaft and that the belt is routed correctly
'03 Marauder 300A / Forged 11:1 Eaton @ 17 lbs - 87 Octane
decipha @ EFIDynoTuning