Hook 12 V dc directly to the pump and see what happens.

Fuse in line with the pump has not been needed since the 123s. They had a design flaw in the 123 where a shorted monovalve or aux pump would fry the CCU controller.
That was fixed in the 124 and later systems with a current limiter that shuts down in the event of a short.

I still cannot fathom why someone just cut the wires unless the pump motor failed shorted.

I took the aux pump out of my 1985 300D because it was spewing a little coolant out of the shaft seal. Since replacements cost >$100, I replaced it with a short length of 5/8" silicone hose (ebay) between the metal tubes, and blue so it looks cool. I get plenty of heat, at least when the quirky temp controller and/or servo-valve decide to respond (my next task). I never saw an electric water pump in any other car I owned, so figured a quirky German thing and not needed.

Just to report back....Needless to say, it's been pretty cold as of late....down to low single digits. I've concluded that I have ABSOLUTELY NO NEED for an aux water pump on my W210. At idle, you can tell there's a drop in vent temp, but it's not nearly as dramatic as it is on a W124....it still blows pretty warm.