John, decoder outputs 10.5V on all outputs. Well at least in my case they will. The spec says Vinput minus 1.5 volts. I assume there's diodes in the circuit to effect a 1.5V drop. My source will be 12V battery, or track power.
I found similar to the little guys you posted, although I just remembered that I have a couple dead dPS1 boards, maybe I can steal a relay from those. They're 9Vdc, right?