Thanks to your help I found this in the manual:
Zeus Series: microZEUS with Flying Bus Boards
Using the –12V Rail:
The –12V rail uses a switching regulator. This switching regulator needs to
have a minimum load of 100mA (out of 500mA) at any given time. The
uZeus has a factory setting to self consume this current. If your uZeus is
powering more than four (4) analog modules you can then disable this
setting if desired to make this 100mA available for use by your modules.
With the uZeus powered o , look for header J7 (located below the blue
resistor) and remove the jumper. Re-insert the jumper such that it comes in
contact with only one pin. Once reinstalled in the system, the uZeus will
provide the full 500mA of –12V power for your modules.
It's exactly the fifth module 🤣 and the rack would need 250mA on the - 12V rail. I hope this will do trick. If not I might ask again 🐒