If a device has less than 4GB of total storage, I would not buy a map update for it, especially since the Streetpilot series is not auto-offered a map installation to SD card: https://support.garmin.com/support/search Support/case.faces? As pointed out, newer nuvi models can be found for 0-150 that include lifetime map updates and offer many more features than the older Street Pilots.
Really - it is worth it to spend a little more to get lifetime maps and traffic on a new model which will have more internal storage and the ability to add a SD micro card.
Locate the "Reset" button under the face plate and press down in order to restart the device. If the fuse blows on the GPS, you will need to make a replacement using an ACG/3AG 2 amp fuse.
Unscrew the adapter cord at the end and remove the fuse found there.
You can get used old-style GTM-20's on e Bay that will work but as noted above, by the time you pay for maps and a traffic receiver, you are pretty close to a new device.
Garmin Street Pilot C340 is a navigational device that launched the popular C series of Garmin GPS units.
It offers text-to-speech navigational directions, maps, traffic information, warnings and more.
Some models of Garmin GPS systems, such as the Street Pilot c340, allow you to update the maps.
Updating your maps periodically ensures that the directions your device gives are always accurate. Visit the "Maps" page for the Street Pilot c340 from the Garmin website.