First, about the continuity, the coil of the solenoid was a wide-open circuit! No continuity between the ground(-) of the battery and the tip of the connector. Definitely D.O.A.
YEE-HA! HE's running smoothly again. Definite thanks to everyone for the accuracy of your suggestion.
The last try I used a pair of medium-sized 8" Vise-Grips. The first three attempts slipped but the last grip was super tight and I belted it with a 2Lb sledge about five times to crack loose the threads - Voila! it moved and the threads let go. I really almost gave up, but I said to myself just one more try and three's a charm - four does the trick!.
Here's the long and short of it.
1. To get at this solenoid on my YR2000 idTD you have to remove; The Turbo Intercooler ducts (Pipes), Drop out the Radiator Fan Assembly (this gives you another precious inch of spanner swing) but be careful to remove the wiring harness all the way down to the radiator temp sensor. Mark the connections because there are polarities and two fans that need to be back in their place, in the end, Remove the Accelerator/Cold start bracket and drop the assembly down as far as the accelerator cable will allow, but remember you will also have to loosen and slide the cold start shaft out of its lever first. It also helps to remove the Air Filter intake pipe that connects to the frame above the radiator.
2. A closed-end spanner would be the tool to use here but FIAT has placed the solenoid too close to the fuel pump housing to do this. The open end of the 24mm spanner may also be too fat. Fortunately, I had borrowed a modified spanner that had its ears trimmed a bit. Nevertheless, I didn't use it to remove but to tighten the new solenoid back in place.
3. I suggest the Vice-Grips. Be careful when turning the solenoid out as the fuel lines are right there at the end of the swing and can be damaged. If yours is stuck give the Clamped Vise-Grips a wallop with a substantial hammer a few times. It worked for me!
All this and 15 hours later, to remove a 15 Euro part! But it is the gatekeeper of the whole enchilada! Without this guy, nobody goes anywhere.
Have fun with this one - it's a knuckle mangler!
