An addendum to our tech tip of 8/4/10, from Sweetwater’s own Troy Hartman:
Another suggestion for Plan B at the bottom: You could still use the battery that was mentioned earlier. Just unhook the wires from the amp and speakers. Connect one set of leads to a battery. Go to the other end and use a voltmeter to determine the positive lead. That way you don’t have to run another set of wires back to the amp.