Connecting NMEA instruments


13 May 2001
south west
i want to connect up my Garmin 120 GPS with my JRC 1000 radar and my Navico Autopilot. How do I connect up the NMEA interfaces - is it a case of just connecting the wires? and which goes to which (Output and input etc). What about earthing? The manuals offer no guidance on connecting up these instruments. Thanks in advance.


Active member
30 May 2001
East Coast, Woolverstone
Relatively easy, if you have manual for Garmin it will give you colours for common, Data out and Data In. 3 wires in total.
Connect Data out and common to the radar and autopilots Data in and Common respectively. The NEMA bus can drive at least 3 inputs from one output. But you cannot have more than one output driving one input if you get my meaning, the sentences sometimes get overwritten and it all gets very intermittent. You may need to alter the NMEA output type on the GPS but mine worked straight away without alteration, theres only 3 choices so its easy to work through them.

Test by setting a waypoint at 180 degrees to the way the boat is pointing and instruct the GPS to goto it. the Radar should show a lolipop (waypoint) and the autopilot move the tiller. If that happens you've cracked it.

Good luck.


The NMEA plugs at the back of your gps are 6 pin ususualy data 1 & data 2 if you look in the book which comes with the gps you will see each one has been dedicated.Data 1 is normaly dedicated autopilot and radar.There is a problem with voltage levels sometimes so you need an interface which is nothing more than a I.R.transmitter and receiver in a small 1 is shield 2 send 3 return for the autopilot you will need to do some research for the radar to find out the series.ok.

double trouble