whunter:
I found 0V at the Aux Water Pump at Def.

But then I found a cut in one of the wires. Soldered it, and now get 12.45V. Thanks for the advise.

Funny that I connected the old Aux Water Pump and it wouldn't spin. Is it possible that the old pump siezed and fried the wire??? (If so, good thing it did so in a visible spot, not in the joy of the fuse box.)

The voltage at the Mono Valve is 11.87V in Off & 1.23V in Def.
The resistance is 13.7 Ohms. (Which as per Mercedes Manual should be between 11 - 19 Ohms.)

THANKS AGAIN!