Step 2: Create the power supply
Because this is one of the simplest steps I put it first.
1. Cut 2.5 feet off the end of the intercom wire.
2. Strip 1" off each end of each of the 2 wires.
3. Connect one of the stripped off ends of the wire to the 9v battery clip. You can connect the wires like I demonstrate in the crummily drawn diagram.
4. Snap the 9v battery clip onto the 8 AA holder.
5. Unscrew the 1/8" mono plug, slide the black plastic piece onto the other side of the 3ft section of intercom wire, connect the 2 stripped wire ends to the mono plug (make sure they dont touch each other, you can separate them with a piece of electrical tape), slide the black plastic piece over the connection you just made and screw it back onto the plug.
6. Put the batteries in their holder.
When you are done you should have something that looks like the 3rd picture below.