Do I tie the commons at the transformer outlets, or should I tie the Z1000 common to the TIU output ground?
Connect the Commons at the transformer outputs.
I did this and got some strange behavior. The only ground that will switch the DZ1000 properly, either from the controller or from the isolated track section is the Z1000 ground - independent. If I common the TIU fixed 1 output to the Z1000 ground, the breaker on the Z1000 pops. If I ground the TIU fixed 1 input (Z4000 output gnd) to the Z1000 gnd, the Z4000 will read 1.4V when the handle is at minimum, and won't advance past about 16V at max handle (seems to load it down). Also, at some point, the 20A input fuse for the TIU channel 1 blew (not sure when, because I was focusing on the switches, and not running a train.
The only way I can get things to run properly is to operate the switches from the 3A 14V tap on the Z4000. Is 3A enough to run the about 14 switches on the layout, realizing they don't all operate at once and only have momentary current flow?
I don't understand why I can't common the grounds for the Z4000 and Z1000. They are both common vintage, both plugged into the same extension strip, both using polarized plugs, and I previously did the phase test, and they were in phase when wired per the color coding.