Weird is that upper voltage level is exactly 1V over battery voltage and lower voltage level is exactly 1V over zero.
Can you confirm that you have zero volts on channel B when disconnected or connected to ground? Thinking of possible Zero offset case. Or measure with other channel.
If that is OK then I would suspect faulty alternator since the over voltage can only come from regulator. Could you also measure control wire signal when disconnected (measure from alternator side and wiring side).
EDIT: Did some search in google and seems that you have an alternator with two pin connector (L and DFM). Is that correct?
L would be your warning light circuit üand DFM is Digital Field Monitor so it's actually a load signal to ECU and not a control signal.
I didn't see anything wrong from your last captures other than this DFM voltages. What alternator did you fit? It seems that you have some cheap low quality regulator there that is not within specification (at least regarding load signal).