Lowrance HDS7 Generation 1

I have wired mine HDS up to a Garmin 300 AIS (NMEA183) receiver. The AIS indicates it is receiving data (Power light on and flashing receive light) but I cannot seem to get targets on my HDS display. Have also swopped the data wires/polarity around but still no joy.
In the HDS menu for AIS there is only the option to block AIS target not enable.
Anybody have any ideas.
Thanks.

Maybe speak to John Easton at Fishtec.

From John, Tech. suport at Lowrance, Quote I have no experience with this feature, sorry"

Sorry that should be Fishtec not Lowrance

Maybe communicate with Garmin SA contact number 011 - 7910205 ask for stephen