Thanks again, Jeff. I'm not sure how good my seals are (it's been about 20yrs since I operated it), so I wanted to do a hopefully "dry" run of the system outside of the car to keep the fluid off my interior if it blows...
I didn't want to disconnect the lines, if it worked, to reroute around something immovable. Also, running the switch "backwards" if I was on the wrong side of the 50/50 chance would just be one of those perpetual irritants...