I'm remodeling my master bedroom, and in the process I have to fix some shoddy electrical work from previous homeowners.
It seems that they tapped into the existing circuit to add an exterior flood light controlled by a switch in the bedroom. There is a conduit powered from the flood light's junction box, which continues the circuit to an exterior receptacle, and a buried conduit that leads out to a shed in the backyard.
The original wiring job was haphazard at best. There was an unsecured junction box just floating in the attic. One NM cable and an unsheathed wire marked as hot (red in picture) lead to the exterior flood light box. Unfortunately, I neglected to take pictures of precisely how the floating junction box was wired, but I believe it must have been like in the picture (labeled "unknown"). The light switch had 2 NM cable legs connected to it.
So, my question
In the current state of the remodel, I've got the power in for the circuit, and the 12/2 and floating hot wire to the exterior light. I assume I'll need to replace the 12/2 + hot with 12/3. How exactly do I work in this light switch into the existing circuit, sending both a switched hot leg and a powered hot leg to the exterior junction box?