Only a handful of vehicles made in certain years, from a few manufacturers use a CK wired socket. Sometimes different car and truck manufacturers will change the type of wiring configuration they'll use to power certain turn signal and brake light bulbs. Normally you would have Positive and Negative terminals on either side of the bulb, but the "CK" type wiring is different.

A CK/SRCK socket looks similar to a standard, or non-CK socket, except it's wired as shown below:

These 2 types of wiring configurations are primarily found on 3157 sockets. The position of the contacts in the socket is the only difference. The bulbs and the sockets look nearly identical. The most reliable way to determine what you have is to test with a multimeter.  A keen eye can spot the difference by looking closely at the metal tabs inside the socket on the vehicle.

If you install a non-compatible bulb there's a possibility it will blow the fuse for that circuit and you will have to replace the fuse and install the correct bulb. The other possibility is that the LED bulb will simply not work correctly, without blowing a fuse. It largely depends on the bulb and how it is designed.

 For example, the Sparksmith S3 LED bulbs are compatible with either style. However, the S2 bulbs are not compatible with the CK style socket. 

Below is a list of confirmed vehicles that use CK style sockets:

• 2008-2015 Scion XB brake lights
• 2013-2015 Ford C-MAX outer Brake/tail lights
• 2005-2010 Honda Civic COUPE (not sedan) Front Turn Signals
• 2010 Toyota Corolla front turn signals
• 2005-2015 Toyota Tacoma front turn signals
• 2006-2019 Toyota Tundra front turn signals
• 2009-2014 Nissan Maxima front turn signals
• 2004 Acura MDX front turn signals
• 2005 Nissan Pathfinder front turn signals
• 2005 Nissan Xterra front turn signals
• 2007 Toyota Camry front turn signals
• 2008 Ford Escape front turn signals
• 2011 Toyota Avalon front turn signals
• 2013-2015 Honda Accord Coupe front turn signals
• 2018 Subaru Crosstrek front turn signals
• 2018 Land Rover Discovery front turn signals