There is a lot of detail on the forum on phasing lionel 1033s and KWs for instance, but I found no details on MTHs.
I have three loops powered by Z-1000s and I am adding a Z-4000 to run accessories and various other stuff in need of various voltages (maybe a waste but whatever). Anyway, the Z-1000s phase perfectly (connect the grounds, output set to 10-12 volts each) and basically no voltage on the meter between the hots. In adding the Z-4000 to this group of 3 Z-1000s, I can't get a zero voltage reading between the Z-4000 hot (on the variable handle outputs) and the z-1000s. I read basically pretty close to the output voltage (10-12V) as the difference between the Z-1000s and the Z-4000.
The outputs read near the same independently using a digital volt meter. Even with this reading, I think I have them phased because with the plug from the z-4000 to the power strip switched in polarity, I read 20+ volts. Is this the issue of needing a load to do this correctly?