on the engine3 is really poor, in fact it's labeled engine2. The description of the unit on the webpage states it has the ability to multiplex the gps signal, IOW, you can connect your gps to the ais and the output of the ais will include both ais and gps information. This is typical of most units. However, the documentation
never mentions this feature so you have no clue how to connect it to take advantage of this feature.
Your alternative is to use a second serial port on the PC and connect the AIS to it using the blue wire and the negative from the 12v supply. This port will run 38,400.