We might be going down a deep rabbit hole here…..
I agree! Have you tried putting the MCL2AV in MCL2A mode (by holding down the TIMER button and pressing RESET (SHIFT MUTE) on the BL1000? If I do this with mine, then use SHIFT RADIO 6 to turn it on, the LED stays on and no sound comes out of the PL speaker. However, pressing the sensor’s MUTE button I can hear the MCL2AV’s relay clicking on and off. Perhaps this works for your mute button? I have then put the MCL2AV back in ‘2AV’ mode by holding down TIMER and pressing AV.
Oh yeah that could be a good way to test it. Will try that tomorrow