GPS Guided Robot - GPS not working (works on GrovePI)

After I have received the GPS module (Seeedstudio, the newer model) I tried to make it working on the GoPiGo.
I followed the instructions and changed the cable wiring. There was always an error message and never a position.
Then I tried it on the GrovePi. With some minor program changes it was working.
When comparing the program code, its nearly the same. But when connecting the GPS to the boards its different. On the GrovePi I used the RPiser connection (working) whilst the Serial connection (with the changed cable) is used on the GoPiGo.
In the python programs there is always the interface /dev/ttyAMAO used.
Currently the board is directly connected to a 5V USB whilst I turned the battery off.