An "Open Zone Alert" on a fire alarm panel shows that the wire is not continuous. The fire alarm system, being a life safety system, is always checking the wires to make sure the devices like smoke detectors or pull stations are connected at all times.
Put the BXY-40 back the way it was before trying anything. You need to make some voltage measurements before trying to swap any parts.
For an "Open", consider the panel to be a big continuity tester. The "Open Zone Alert" is saying that a wire is broken or a connection has come loose somewhere.
Use you DC voltmeter and check the voltage on each of the zone terminals on the panel. If one of them shows a higher voltage than the others, that means that electricity isn't flowing in that zone.
Next, measure the voltage at the end of line resistor. (It's usually a resistor, but it may be the BXY-40. Whatever the type of device, it's at the end of the zone wires, farthest from the panel.) If that is zero volts, that means that the electricity isn't reaching the end of line device.
If the zone is showing voltage at the panel but no voltage at the end of line device, you need to find the loose connection or broken wire.