Talk to Brian at Bournemouth Avionics
He installed my 430W and installed two LED lights to show if CDI or GPS mode was enabled at the same time he installed my 430W - he made a point of saying they were needed because they were needed by rules...
or google is your friend
http://www.aero-farm.com/ubbthreads/...page=0&fpart=1
http://www.g1000book.com/garmin-430-...formation.html
Finally, depending upon where your GPS unit is located in the cockpit, you may need an external annunciator installed. It turns out that the requirements in FAA TSO-C146a, are far more specific about receiver location than is TSO-C129a, which governs traditional GPS installations. Specifically, the left edge of the 430W can be no more than 11.8" from the pilot's primary view centerline, and the 530W cannot be more than 12.1" away. Also, the top of the 400/500 series unit can't be lower than the bottom edge of the primary flight instruments. If a unit falls outside of this specification, an external annunciator must be installed near the pilot to annunciate the various receiver modes. The required annunciators are: VLOC, GPS, INTEG, TERM, APR, MSG, and WPT.