That is interesting. My old Airtex pump is just the opposite. With the outlet at 6 o'clock, looking at it like a face, the left post is positive. The check valve is built into the outlet.

If the dribble that gets past the roller chamber has enough pressure to open the check valve, given the 6-9 psi expected from the tank pump, and it stops when you turn on the main pump, then I would conclude the motor and pump are joined and working, but in reverse. Sucking hard on the check valve the wrong way.

Now on the pic and the wiring, I'm lost. What am I looking at, perspective wise? Are you saying there's a better picture somewhere else? I can't make anything out. You might be able to describe in words why you think a white wire turns blue. There should not be either color associated with the main pump unless someone worked on it before and did not have much wire.

Do you have a Bentley, Haynes, or Volvo wiring diagram?
--
Art Benstein near Baltimore

A thief who stole a calendar got twelve months.