Jim,
Yep, you got it..... Use a hot iron, at least 40W, and lay the wire into the hollow end, crescent uppermost. Best to tin the wire first, then apply heat viciously for a short time. When good and hot, add the solder. It should flow nicely.
Because there is a fair amount of thermal inertia in the binding posts, once in place and completed, hold the wire quite still for ten seconds or so as it sets. Failure to do this could move it around during the solidifying process and lead to a dry joint.
The positive wire (a misnomer, better referred to as ACTIVE) is marked 'signal' on the pcb; the negative wire (better referred to as ground) is so described also on the board and goes to the outer conductor of the RCAs, the 'frame'.
Cheers,
Hugh