I know, bit of an old thread but I figured out how to read some of this stuff. What you'll want is this:
#define EVT_MASTER_WARNING_RESET_L (THIRD_PARTY_EVENT_ID_MIN + 509)
All PMDG aircrafts with an SDK has this line in it and this 5 digit number:
#define THIRD_PARTY_EVENT_ID_MIN 0x00011000 // equals to 69632
What you do then is take is add the two numbers together to get your 5 digit code to enter into FSUIPC. 69632+509=70141
Go to FSUIPC select the Buttons &Switches tab. Press said button. Off to the right, check Select for FS Control. In the drop down menu select Custom Control. A new window pops up. Enter 70141 and hit ok. Under parameter, enter 1 and hit ok. You should now be able to press the button on your controller to control the Master Warning Switch. Search for these functions in the SDK that begin with "#define EVT_" and end with "(THIRD_PARTY_EVENT_ID_MIN + 509)"
I've already programmed the 4 overhead start switches to both of my saitek throttle quads. I've programmed both No smoking and seat belt signs to my custom panel as well as the autobrakes using this method.