why do you want to have the ability to turn off just the SS module? Battery drain, don't plan on using SS except when hunting for the fish? Are you planning on not using the down scan except in search mode as well? The installation instructions give you two options on wiring up/powering the SS module and deals with the "yellow" wire IIRC.

I usually have SS or DS showing even when longlining, as I like watching the "flat screen" on my HDS 8.