TIU AUX power input, Z4000 14V accessory output - how do I get the polarity right?

Does someone know the polarity of the TIU AUX power input plug?  IE should the inner post be black or red from a Z4000 accessory output.  I couldn't find the answer in the DCS companion book.  Just that the polarity needs to be the same for the AUX INPUT and any other INPUTs you're driving from the Z4000.  I wish to drive the 4 TIU channels via 2 Z4000s, and have AUX power on the TIU via one of the 14VAC accessory outputs (which is not being used for anything else).

Thanks!