Music Man Amps

Hello, first time posting here, but I've been lurking since way back, when I first biased my Sixty-Five. I've been using Music Man amps for recording and live gigs for almost a decade now, and I'm still diggin them : ) Anyways, I have a rather simple question, but I just wanted to be sure. Per the RD50 manual, and some threads here, it says that if you put a blank plug in the ext. speaker output, the main speaker output will be lowered to 4ohms. The only question I have is, does a blank plug just mean any 1/4" plug that's not connected to anything? Thanks in advance, and I'll try and get a pic of the rig up here!