300XL Approach Mode problem

[DGlaeser]

I've got a 300XL serial connected to my GRT Sport for the CDI, which works great. I don't have an external CDI connected (the wiring is installed in the 300XL connector, but just coiled up behind the panel at the moment). I have an AK950 Annunciator panel.

Problem: When I select an approach, the unit never Arms or Activates the approach. Neither the 'Arm' or 'Actv' lights ever illuminate (but they do on a press-to-test). It sequences the waypoints just fine and goes from 5NM sensitivity to 1NM sensitivity, but never goes to .3NM sensitivity. It warns me that the approach is not activated. No RAIM warnings (which would prevent an approach from going active). Pressing the Approach Mode button on the AK950 does nothing.

Not having the external CDI prevents me from selecting a course when in 'Hold' mode, but as far as I know that is the only thing I would need the external CDI for.

Any suggestions?

[DGlaeser]

I re-did the installation configuration and discovered that the APPR button was shown as 'not installed'. Pressing the APPR button caused the unit to recognize it, and now the ARM light comes on when I enter a nearby approach (on the ground). I'm sure next time I fly it will work as expected.