FasTrack Block power wiring help

You generally want the "black" or "U" terminals going to the outer rails of each loop and tied together.
You also generally need the "red" or "(ABCD)" terminals going to the middle rail of each of your loops. This is the wire that needs the SPST switch. That is, put a switched wire to each loop from the transformer and don't worry about trying to "jump" the block section.
If you wish to do this anyhow, you need to have a switched wire from the blue middle rail to the yellow middle rail and a switched wire from the blue middle rail to the purple middle rail. This assumes that the blue rail is constantly powered from the transformer. Note that the blue section can not be independently switched in this scheme since that would also switch the other two sections.

Looking at the diagram:
"A" and "D" do not do anything because they are on the same side of the block.
"B" or "C" would work, but no power is coming from the blue section, so the yellow section is dead. Also, you would only need "B" or "C", not both.

Note that you might want more than one feed to each loop. These would be connected between the switch and its associated track (or from center rail to center rail on the same loop).

I find your diagram a bit confusing, but it looks like D&A are on the same loop.

Instead of jumping from track to track, it would be better to run a hot from your transformer to the toggle in, then out to the track in each case. Commons can all stay connected, and theres no need to isolate the outer rails.

Super helpful, thank you both. Hopefully, this v2 diagram makes more sense? And yes, I have a common ground for all of the loops.

Thank you for taking the time to help me! Much appreciated