For completeness, from the install manual:
Outputs 7, 8, 9, 10, 11, 12, 13, 14, 15, and 16 are low current, positive (+) voltage only, for driving LEDs, relays, etc. Outputs 4,5, and 6 ARE NOT available from the main board. They can only be accessed with a data bus Output expander set to address 1. This expander will replicate all the main board outputs, including outputs 4, 5, and 6.
Without an expander, you might be able to use 4,5,6 as a non-physical output, i.e. an internal flag for rules. Never tried.
