Originally Posted by femsailor
thank you, but do i turn the switch to regulator or rheostat and how far do i turn the dial?
I would set it on "Regulator" and then measure the output voltage as suggested by Djmarchan. That would be the 'default' mode for an alternator to charge an SLA battery (like it does in a car), and if that does not work, there could be something wrong with the alternator or the regulator.
If that works well, then I would move on to check the Rheostat option (the rheostat would probably be a fairly large disc-shaped item with a central shaft; the disc probably over 2.5" in diameter; it should be rated at least 50watts to handle a 4amp field current
; preferably higher). As you turn the rheostat shaft, the output voltage of the alternator (measured at the same output stud) should vary accordingly. Try to keep the output voltage under 15volt as you turn the dial. Be careful not to over-charge the battery with this option.