Garmin GRA 10 rudder adaptor cable
With the GRA 10 Rudder Angle Analog Adapter aboard your vessel, you can give new life to your old gauges by making the transition from analog to digital. This simple-to-install adapter takes the data generated by traditional analog gauges and converts the data into a NMEA 2000 signal so you can create or expand your network without replacing all of the equipment on your boat.
Connect to Your Network - With the Garmin GRA 10 adapter, you can convert analog information provided via the rudder-angle sensor (not included) on your boat to your NMEA 2000 network. The GRA 10 allows you to observe rudder-angle information on compatible Garmin display devices connected to your NMEA 2000 network.
Find the manual here