Don't know if this has been asked before but my buddy has a 12" Hummingbird SI unit but won't have it for this weekend. My other friend has a smaller Hum SI unit but we just wanted to know if all the hookups are compatible to the smaller unit. I was thinking they may all be the same cables but was not sure. Any help would be appreciated. Thanks

Yes they will interchange. If they are 98/99 series.

Okay so the two we have are the 1198 and 797. Does anyone know if these two are compatible as far as hookups for power and GPS go? Thanks

the cable ends are the same but the plus are not. you can change them .take out the Phillips screws and just change plug cap.

The cable collector for the 797 is in the quick disconnect mount.
The 1198 cable collector is cube shaped and snaps on the back of the unit.

The power cords are different. The 1198 has larger conductors and a built-in choke (PC-11). The 1198 uses more amps.
The 797 has the PC-10.

The 1198 uses a HDSI transducer and the 797 uses a Compact SI transducer.
The HDSI transducer will give the 797 sharper images and the 797 transducer will produce less sharp images with the 1198.

The 797 is single frequency SI (455 kHz).
The 1198 is dual frequency SI (455/800 kHz).

The GPS antennas may be different depending on the age of the 797.
The standard for the 1198 is the 50 channel GR-50.
The 797 may have that one or the less accurate GR-16.

The only 12" screen hummingbird makes is the Onix series and I don't know if the have the same hookup. The 1198 is a 10" screen just making sure the model number is correct

Thanks everyone and I do think it's a 10" and not 12"