I'm assuming you have the Comissioning
guide (Document 81214-2), there's tons of info in there (you can download from the Raymarine site if you don't have it).
If you can't get anything useful on the display, check the seatalk connections then the Euro-style fuses
on the S3 brain, there should be spares inside the panel.
There should be two seatalk inputs on the brain, try the other one.
You are going to need a rudder angle sensor for this set up though, seen a few on Ebay for reasonable money
Enjoy Buzzards bay, getting any swells from IGOR up there ?