But what is very important is if the socket the bulb fits into is a wired for CK or non-CK.
Why is this important? Let me explain..
Polarity Sensitive represents the idea that the item at hand (LED, HID, Capacitor, etc) can only be connected in one way to work correctly, positive to positive - negative to negative. If you connected them incorrectly (negative to positive, etc) than they will not operate or damage the item.LED bulbs that are 3157 and are connected into a 3157CK socket will damage the 3157 LED bulb. So this is why it is important to connect a 3157CK LED only bulb into the 3157CK wired socket.
How can you tell if your socket is wired for CK or non-CK? Using a test light or multimeter you can find out which metal connection on the socket is positive and what is negative. Check the images above and below for comparison.