Chris,
It is totally do-able! Obviously, since all of these third-party hardware developers manage it.
What Pete is saying, I think, is that FSUIPC doesn't support the lighting up of LEDs associated with the FS interface, unfortunately. In other words, these annunciator states are not available to FSUIPC - otherwise they could be grabbed and output to the hardware.
I came up against exactly this problem in developing my Level D 767 cockpit, which is absolutely littered with annunciators, and the solution was in the LVLD SDK, ably assisted by Nico Kaan's FSCONV program which provides the required offsets for FSUIPC which aren't supplied in Pete's original install - but these are specific to the LEVEL D 767 product!
I guess Nico's work was only possible because of the existence of the 767 SDK, so if your addon doesn't have an SDK, you will probably never find the offsets.
You could try scanning all the data from FS, made available in FSUIPC, using FSInterrogate (part of the FSUIPC SDK) and see if you can find the indicators in there, although I tried that with the 767 indicators and got nowhere. I just don't know enough about FSUIPC to say if that would work or not. I'm guessing, from Pete's admission of lack of experience in that area, that it might not be as simple as that! :cry:
EDIT!! I've just realised that Pete's admission was nothing to do with interrogating annunciator states using FSUIPC. Of course he knows exactly how we can do that! The issue is with your hardware, and his note posted before he selfishly left us to actually do something else for a short while :D was simply to say that he doesn't know how your hardware is set up to switch a light on! And of course FSUIPC will support the interrogation of annunciators, if the offset for the annunciator is known. Sorry, Pete! :oops:
Alistair