How to Tell the Polarity of Speaker Wire
A speaker wire seems like something that's very easy to use--just connect it between your amplifier/receiver and your speakers. There is one crucial aspect of using a speaker wire that shouldn't be ignored, though, and that's the polarity of the wire; in other words, which lead is "positive" and which is "negative." In truth, there's no difference between the leads of a length of speaker wire in construction, but you need to know which end to connect to what part of your receiver.
Look for markings on your speaker wire. Many speaker wires come with markings on the wire showing which lead is positive. In most cases, this is accomplished by printing a series of "+" signs on one of the leads.
Examine the wire for other markings. Red is used almost universally to indicate a positive lead or terminal in electronics. A marking such as a red stripe will indicate a positive lead.
Look for color-coded insulation. In the case of the illustration, the red jacketed lead will serve as the positive lead.
Make a decision on polarity. In some cases the wire is color-coded, but with no indications as to which should be positive and which negative. Simply decide on which lead will serve which function, and be consistent in your application. Jot down what you've decided if you think you'll forget.