If I understand correctly you have an alternator which requires an external regulator and you have not bought one for it yet. If this is true then it is doing very little. The field coil is what makes the magnet, so that spinning the rotor coil in that magnetic field makes electricity. You can directly plug
the field connections to a 12 volt source and the the field coil makes a magnetic field, then alternator will produce its maximum current
, this will result in frying your batteries. If the field contacts are shorted no magnetic field, no produced electricity. If they are open a little unknown amount of electricity is made by the rotor inducing a magnetic field in the field coil (This discovery was made trying to troubleshoot a car failure in the middle of nowhere on the highway.)
The simplest regulator is an automatic switch for turning the alternator (powering the field coil) on and off at a preset voltage. So if the battery is low, it is on, when the battery is at the voltage that you don't want to exceed it turns off.
The combiner is another automatic switch, it has nothing to with controling the alternator. It mimics you looking at a voltmeter. When the voltage is high enough on the battery that your alternator is attached to that you know it is charging, you connect all the batteries together so they all charge, when the engine
dies and you see on the voltmeter that the voltage decreases below the charging voltage, you separate the batteries from each other.