The existing documentation and videos are great (really) for those transitioning from a traditional wired alarm system that is wired in typical fashion. But if that use case varies (for example, in my case I am converting a home automation system, not just alarm), or someone finds some atypical wiring, just a little more documentation is needed on the specifications on the connections.
In my case, the system I am replacing has a bank of voltage inputs which can accept 4-24V AC/DC to which my sensors are connected. For this reason, 3-conductor wiring was used for sensors that required power. Motion is indicated by presence/absence of +12V on the third wire. No fourth wire needed.
I assumed (very incorrectly based on the smoke) that a zone configured for input could accept +12V DC. My conclusion is that you cannot use voltage input, only dry switched input. This is not altogether terrible though because I don't need to rewire the house, but instead have a bank of 12V DC relays that open and close the circuit that is connected to a zone. Right?
What would certainly have helped me and anyone encountering atypical scenarios is just a list of connections on the two boards and what they expect or provide. I'll provide an example of what I mean. Please note for those reading this that you should NOT assume this is correct and it is certainly not complete! I am just providing a possible template and my best guess.
AUX+ provides +12V DC out always on. Max load xxxx.
AUX- provides -12V DC out always on. Max load xxxx.
SIREN provides +12V DC when Siren activated
When configured for output
Zone # provides +5V DC if and only if zone is turned on
G provides -5V DC
When configured for input
Zone # and G are switch inputs that sense closed or open circuit. Polarity doesn't matter. Zone # provides +5V DC always. Circuit must NOT have another power source.
Also adding a crude picture of what I now believe to be the case: