Official free software is rare beyond drivers. But third-party, open-source communities provide excellent alternatives.
Format the SD card to FAT32 (not exFAT or NTFS). Maximum usable size is 32GB for older Cartrek 400 units. Free Software Download cartrek 400 navigation
Official support for legacy CarTrek models can be difficult to find directly from a single manufacturer site, as the brand often rebadged generic hardware. Here are the most reliable ways to source downloads: Official free software is rare beyond drivers
The CarTrek 400 is a legacy GPS navigation device. Official software downloads and map updates are no longer actively supported by major platforms like Naviextras Update Methods for CarTrek 400 Free Software Download cartrek 400 navigation
The map you downloaded may be "transparent" (only contours). Download a "routable" OSM map which includes streets.