Wiring

[steamhead]

I concur with Fred....Without really knowing the particulars of your layout, there is no reason to do this circus-act sort of thing. Your yard shouldn't be isolated from the rest of the layout, it can be just one more block in a series of blocks that make up the whole layout. Your walk-around can be one of the two power packs that can control any one of the blocks (including the yard) in the layout.This way, you can work the yard with one of the packs from the MRC unit, and when a train is ready to leave the yard and enter the main line, just assign the walk-around to the yard and the mainllne blocks you will be using, and exit the yard "seamlessly"...No flippin' switches at just the right time; no sudden jerks as you bridge two circuits, no shorts...no nothin'....Just good ol' enjoyable railroading....

 

[Santa Fe Jack]

I have my DC layout set up with common rail, 11 blocks, and four separate controllers (two dual power packs). No problems. I use 6-position dual pole rotary switches, with one pole switching the power (since only one lead is needed in common rail) and the other pole switching indicator LEDs so that I can see which power pack (red, blue, green, or yellow) is powering each block. Each block has its own rotary switch, as does the turntable track power.

Though admittedly I don't know if that is much help to the OP. I don't quite understand your diagram, Prof1000. I'd think you'd want the insulating joiners on the lead between the main and yard, not on the main itself.