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.
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).
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.