You guys need to go into your (for Lowrance, Humminbird is probably similar) SETTINGS, NETWORK, and enable (meaning click on the box or bubble) NMEA 0183 OUTPUT – sometimes it is one bubble to highlight, sometimes it is a list of SENTENCES, depending on the unit.
What happened is, the NMEA 0183 output is off by default, so installing a new unit or having done a hard reset on an existing unit, you have to tell the unit to output the NMEA data. The wiring is already there if it ever worked before.
The NMEA network is normally built by Bass Cat and the sonar units are normally installed or set up by your dealer. Although I’m sure this can vary.
It’s stupid simple, once you figure out where in the menu to find it.