Chosen Solution

I need to add an RCA plug to a subwoofer to attach it to a Panasonic model SA29 audio system. How exactly should the [lug be soldered on to the existing wires?

@jwphelps bit confused by your question;-) The Sleeve on the RCA connector is ground and center connector is positive. This does correspond with the output of the SA-PM29 and other models. Not sure if that is what you are trying to ask.