How do I know which one is a positive terminal?

Answer by  john11 (617)

If powered, the multimeter will help because you can measure voltage. You can put the positive terminal of the multimeter on the device terminal you believe is positive and attach the negative multimeter terminal to the other device terminal. If the multimeter reads positive voltage, then your assumption is correct

Answer by  mprobi (28)

A positive terminal can be determined with the use of a DC Multimeter. The DC multimeter will indicate a positive or negative voltage depending on which terminal is on which lead. A positive voltage would indicate that the red lead is the positive lead.