[Guy]

Interesting project!

I think that your IR eye wiring may be incorrect:

• On the MCL2A transceiver the Green wire is for +5v.  (Green became IR data in later devices, such as BS3 sensor)
• I think that the White wire is IR data (but if that doesn’t work, try Yellow!)
• Brown is indeed Ground

Leave Grey and Yellow (or White) unconnected.

Guessing again, but to test the IR-eye connect a 5v supply to Green (+5v) and Brown (Gnd) and transmit with a B&O remote.  A red LED should glow in response.

However, despite all that I have said above I am unsure whether the Passive will respond at all without an ML connection.