3157 vs 3157CK - What is the difference?

3157 vs 3157CK - What is the difference?

3157 bulb base image  3157 CK bulb base

The T25 wedge bulb is a very common bulb size that has many different other bulb number associated with this style. The main bulb number is 3157. Some manufacturers change the number when they change some small aspects about the bulb. If it is a long life bulb the bulb number may be listed as 3157LL. If the bulb is an amber coated bulb then it may be listed as 3157A. If you have a 4057 bulb that fits into the 4057 bulb socket, any of the bulbs listed in the images above will work. When it comes to LED the other incandescent bulb features are not important. 

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..


First question might be, why doesn't it matter with incandescent bulbs? Reason is because an incandescent bulb lights up using a coiled wire and does not matter what wire is on the positive or negative as long as there is at least one positive and one negative one one coiled wire. There is no "polarity sensitive" operation with incandescent or halogen bulbs, only with LED and HID systems.

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 multi-meter you can find out which metal connection on the socket is positive and what is negative.  Check the images above and below for comparison.


3157 bulb socket


We offer LED bulbs that are for non-CK and CK, as well as bulbs that work in both applications.