You need to activate the maps on the SD card too.
Here is what you must do:
First copy across the ttgo.bif file from the internal memory onto the card, then run FastActivate from the root of the SD card. Confirm if a .dct file has been created in the map folders on the SD card. If so, this means the maps have been activated on the SD card. You will then be able to switch maps on the device.