1. Judging from the structure of the coil, there are usually two terminals on the coil, one is the positive terminal and the other is the negative terminal. Some coils are also marked, such as "+"and "-",to indicate the positive and negative poles.

2. Test with a multimeter: adjust the resistance or voltage range of the multimeter to a suitable range, and connect the positive and negative poles at both ends of the coil respectively. If the reading is positive, the positive and negative electrodes are connected correctly; If the reading is negative, it means that the positive and negative poles are connected backwards.