Diagrams for connecting bare wire of GPS (NMEA 0183) to serial port DB-9 numbered pins for read, write, grounding

Article HD25700, August 13, 2015

Exact details of wiring a given NMEA 0183 product to a computer's DB-9 serial port may vary, but diagrams in this article are a useful guide for improvising your wiring plan.


Some GPS or other NMEA 0183 devices have bare wire connections that a customer may wish to connect to a computer's DB-9 serial port. 

The following diagram, courtesy of long time Fugawi user Dr. Vonesch of Switzerland, illustrates an example of connecting a Garmin 45 GPS to a computer. In the example illustration, the wiring coloring is specific to the Garmin 45. 

Example serial cable to PC COM port pin out diagram

Other GPS devices may have different wiring colors for transmit / read / ground. Consult any given GPS product's literature for information on wire coloring corresponding to function. The important aspect of this explanation is that on the computer side, the transmit / read / ground are universally assigned as pins 2, 3 and 5.

To avoid the task of soldering and difficulties with the physical connection to the DB-9 serial pins, various products like the Actisense OPTO-4 take bare wire inputs from NMEA 0183 devices at one end and offer a DB9 serial connection for a standard PC at the other end. If you are unsure about what color of wire coming out of a NMEA 0183 device represents what function, either consult the manufacturer of the NMEA 0183 device or get help from a marine installer (who has likely dealt with these issues many times in the past and had the equipment to determine the correct wired connection).

Actisense OPTO-4 wiring diagram taken from PDF user guide

For a deeper understanding of serial connections see this third party help article on pin-outs and signals with 9 and 25 pin serial connectors.