ok , you have a valeo isolated ground alternator. so the B- should be to ground, The W terminal is the tach and the othe6 rone normally marked "61" is the ignition/idiot light/ field coil excite, this should have power on it, when the ignition/starter key is turned.
If your battery
positive cable runs through a diode isolater, then there will not
be power ie 12V on that terminal with the alternator not running. However power should appear once the alternator spins up. If not either (a) The field /excite supply via the "61" terminal isnt powered or (b) The diode trio is gone on the alternator, this could happen if the battery
switch was disconnected with the altermator running.
ogh 61 could also be labeled d+