You could have the wrong data format set, in addition to the baud rate make sure you are using a source set to 8 data, 1 stop, and no parity bits. NMEA 0183 is normal message format expected, some "232 Aviation out" formats also work.
For the ACK manual:
No GPS data is being received, the ELT test light does not flash, or LED stays on: Check that the data being sent to the ELT meets the data protocol in Section 17 of this manual. Connect test LED to pin 4 and ground of the cable providing GPS data and power (page 8 Fig 13), test light should flash. If not, reverse test LED and if flashing retry test lead on ELT.