How can you tell if a wire is positive or negative

This is your positive wire.If the tester lights up, or shows 120 volts, you have found the positive wire.Look at the reading to see if it's a positive or negative number.Think of the wire color as a guide line as to which you should test with your volt meter first and what you should expect to see in your verification.Second, the negative terminal is usually smaller than the positive terminal.

How do you know which wire is positive and negative?Plug the red lead into the port labeled with the volt symbol, which is v. 3.The positive side is what the compass indicates is.