Wiring question for washer/wiper switch

[Tim240Z]

I have converted my washer bottle to take a pump which I attached to the bottle/reservoir (made a 14mm hole near the bottom and mounted a pump from an old 3 series BMW). It works great manually energizing it, but I cannot figure out the wiring at the switch so that I can wire in the new pump and 'un-wire' the old non-functional one.
The switch has 3 wires: Black(Bl), light blue (LB), and Dark blue (DB).
The Bl and DB are energized all the time. The LB doesn't seem to ever get power. I noticed that when the button is pushed to activate the washer pump, the switch case gets energized (???). If the switch case is not grounded the wipers will not activate. What I can't seem to figure is, which wire can I tap into to provide power to the new pump?
I have a wiring diagram which shows that the pump and wiper motor appear to be all one unit (I have never pulled either out of the truck to see what it looks like).
If all else fails, I will just run a new "OFF--momentary-ON" toggle switch, but I would rather use the existing one as it also fires up the wipers when pushing wiper fluid.....

Any suggestions?