Hi,
this is correct for your alternator with internal voltage regulator, means D- and DF is connected internally.
I assume that you have a problem with your charge control light or the wire to/from that light. 1.6V is not enough, that means only ~50mA. You need at least 300mA to excite the alternator.
You should take another/external lamp with 4W and connect this to the alternator and test it (+12V switched).
Some alternators (with internal voltage regulator) have an additional connector indicated with "L" (+12V switched) to excite the alternator.
Be careful, don't connect or disconnect your cables or battery with ignition turned on.
Can you tell us what type of alternator you have, maybe with a picture!?
...WRe