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Difference between 3157 and 3157 CK

You may have noticed that your 3157 or 7443 replaced the bulb with a CK, SCK, SACK, SRCK. This means your vehicle uses a non-standard 3157 or 7443 bulb. Although they look the same in appearance, the difference is in the way the sockets are connected. In some years, only a few manufacturers produce cars that use CK wired outlets.

Before discussing the differences in sockets, let's look at the effect of installing the wrong bulb. Installing a CK or non-CK bulb on the opposite socket will not work properly. Worse, they will break the fuse that protects the particular lighting circuit. If you have already encountered one of these problems, then it is likely that your basic type of light bulb is incorrect.

You might ask, why doesn't this affect incandescent bulbs? Incandescent bulbs use heated coils to illuminate, requiring only one positive contact and one negative contact. From an electrical point of view, they are not sensitive to polarity. Polarity sensitivity simply means that a light bulb can only be inserted and contacted in one way to work properly (from positive to positive, from negative to negative). Most LED bulbs are polarity sensitive, which is why it is important to make sure that you have the right bulb for the outlet.

Although the two sockets look the same in appearance, the difference between them is the location of the ground point in the socket. The best way to determine if a socket is CK is to use a test light or multimeter to determine which metal contacts on the socket are positive and which are negative. Check the image below to compare your socket type.

Note: Remove all taillight bulbs before testing, otherwise the filaments in the brake circuit will be considered “false ground”.

An easy way to protect yourself from installing the wrong bulb is to use our new 3030 Series bulb. The new bulb is not polarity sensitive and will work in standard, and CK wired outlets. At 950 lumens per bulb in an all-aluminum enclosure, the 3030 Series is a win-win for you and your vehicle!


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