Would anyone happen to know which of the two wires to a 450 SL windshield washer pump is +? The choices are solid wire and striped wire. Ordinarily there are several ways to check but in this case I can't use them.

I'm putting the terminals back in the snap case, and need to observe polarity.

There is no power to these wires when the stalk is energized. The fuse is good. What's the next thing to check?