Today I’ve been wiring up my laptop to my GPS, a Garmin eTrex.
I made the connector in the same way as the one I saw on this site from an old discount card. Using the technical specification from Garmin for the wiring I hooked this up to a 9-pin serial port connector.
Thank you Garmin for publishing that useful information. Open specifications are good.
To track where I am, I installed gpsdrive using apt-get. It detected my GPS plugged into /dev/ttyS0 straight away.