I went poking around with the multimeter and confirmed that there is only one wire that goes between the Protec module and the fuel injection module. This wire also shared continuity with one of the wires at the trigger connection (where the distributor would be on a normal engine). It seems to me that it is in fact just the wire for engine speed (or tach).

I have a fully functioning system right now, but knowing that at some point it will fail, I'd like to learn about the system while it is working.

My biggest question is why does everyone say the EFI won't work without Protec. "Because it won't" isn't an acceptable answer to me, I'd really like to understand why.