Add-On plane problem...

Okay, so whenever I get an add-on plane, I use the default 2-D panel from FSX for the add-on (usually the 737-800 panel for large jets). When I fly the add-on, this altimeter/airspeed indicator doesn't do anything:

It always reads 0 for the altitude and for the airspeed. Also, it always reads 29.92 no matter what I set the altimeter to. Is there a way to fix this? It works fine in the default FSX jets...
It always reads 0 for the altitude and for the airspeed. Also, it always reads 29.92 no matter what I set the altimeter to. Is there a way to fix this? It works fine in the default FSX jets...