This article describes how to connect an iPhone running the Get-Console app to a device that is outputting NMEA data over RS-232 using a Redpark L2-RJ45v cable.
The Garmin unit used in this example is a GPS18x LVC - please visit the Garmin support site for details of the electrical characteristics of the device including wiring diagrams (http://support.garmin.com/support/manuals/manuals.htm?partNo=010-00321-31&language=en&country=US )
Note: this solution is for troubleshooting NMEA data output, it will not override any inbuilt GPS in the iPhone.
The GPS unit outputs RS-232 level voltages at 4800 baud. It is powered externally via a USB power supply via the wiring block. Please check the electrical specifications of your device that it is RS-232 compatible as incorrect voltage levels could cause damage to your devices.
The iPhone is running Get-Console, select the Quick Connect option, choose the Serial Cable and set the baud rate at 4800. Press connect. The icon at the top right of the screen will turn green to indicate that a connection to the L2-RJ45v has been successfully made.
The wiring adapter connects the RX, TX, and GND pins from the Garmin unit to the appropriate pins on the L2-RJ45v cable - see the wiring diagram here for a pinout: http://support.get-console.com/solution/categories/5000071223/folders/5000112374/articles/5000626445-serial-port-pinouts-for-rj45-serial-cables
The RJ45 - DB9 adapter available in the webshop http://www.get-console.com/shop/ can be dismantled/butchered to provide easier connection to a wiring block.