Para versiones mas nuevas
http://www.gpspassion.com/upload2/HiddenTrackLogHowTo.pdf Garmin Nüvi Hidden Track Log
This document is meant to bring some light into the shades of logging tracks with some
Garmin models. Shown are screenshots of a Nüvi 760 with firmware version 4.60.
Screens from other devices may look different!
Breadcrumbs
Some models offer a fully accessible method of logging tracks. This is done by the so called ʻbreadcrumbs methodʼ. The nüvi 760 for example store the latest 10,000 points.Once the file is full the oldest points will be overwritten.
The display of these ʻbreadcrumbsʼ is activated under ʻTools > Settings > Map > Trip Logʼ.
This data is stored in ʻ\Garmin\GPX\current.gpxʼ.
This data may however be inaccurate as to that there is a ʻfeatureʼ that tries to snap each of theses waypoints to a road the device knows.
Raw Data
The other way of recording a track log is to log the raw data. Doing so will make the device record itʼs exact position to a log file every second.
The other way of recording a track log is to log the raw data. Doing so will make the device record itʼs exact position to a log file every second. Earlier firmware versions (up to version 2.30) had an option to activate this feature. Unfortunately Garmin decided to remove the menu to activate this in later versions. But the feature itself is still there.
To activate it follow the steps marked with an orange dot:
1. Press on the car symbol.
The display will now display show your current position. 2. Even though there are no buttons press the following sequence 2a-2b-2b-2a.
3. If all went well you should now be seeing an option that says
ʻStart Recordingʼ. Press that to start the recording of the raw track data 
4. Back on the map screen you will now see a stop button at the top of the map display.
This shows you that the raw track log data is now being recorded. That ʼs it, youʼre done.
What's next The log files are created in \Garmin\Logs. Inside that directory a folder is created is created each time the device is turned on or logging starts. It ʼs name will be something like ʻ20090402_191434ʼ. Each of these folders contains several files (gps.bin, traffic.bin, nav.bin). The ones we are interested in is ʻgps.binʼ. It contains the track data.