Going to help a friend install a HDS-8 Gen 2, LSS-2 ducer and structure scan box. Don�t want to put a switch in to turn box on and off. HDS will have power cord run directly to the battery, can we hook the yellow wire from HDS and structure box together and call it good or do we still need to run the pos/neg leads from the structure box to the battery as well? Any help would be appreciated.

Doing either will leave the structure box powered 24/7. Probably not a good idea.

The structurescan module needs the Pos and Neg wires connected to the battery. The yellow wire is the 'wakeup' wire. You can connect it to the HDS yellow wire and any time that the HDS is powered on it will apply +12V to the yellow wire which will power on the structurescan module. You could also connect the SS module yellow wire to +12V through a switch which would allow you to power on/off the module whenever you wanted.