[FSF]Ian and all, I am relatively new to DCS and over the last year I have been learning the A-10C as time permits.  First time poster.  I recently decided to get into DCS-Bios in hopes of putting together a pit of my own.  I have been through much of this thread, your User Guide and put together the Master Caution circuit using the Uno board.  After several attempts, I have been unable to make it work.  I find the IDE software and your instructions to be straightforward, but....     
The LED caution light will not light up (confident I have the polarity correct) and I only see logging in the cmd window when I press the reset button.  I get UFC_MASTER_CAUTION1 when I press it and UFC_MASTER_CAUTION0 when I let off.  I get no interaction in DCS.   
In preparing the sketch, I find some deviations between the example in the User Guide and the IRQSerial template provided in the library.  The line "#include <servo.h> is omitted from the template and the control reference code for LED masterCaution has different numbers (**,**).  I assume this is just a matter of an updated library.   
I admire the work you and others are doing with this and look forward to making it all come together.  I know it has to be something simple, but just don't see it yet.  Any help from you or others to put me on track is greatly appreciated!