The big jumps are to -50 when the fan kicks in. I saw one quick jump to the + side about half way I would guess. That’s probably when it shuts off and takes a split second for the VR to adjust.
Got a schematic of that wiring - specifically of the protected side of the circuit breaker near the starter relay? I’m going back out now to finish up an
oil change and I’ll look at it to see if I follow that?