Without testing we'd only be guessing . complex electronics involved , control module's , serial data communication network's etc...The switch is a input to the instrument cluster microprocessor which is hooked to the C.A.N - controller area network serial data communication network for the computers on the vehicle . This problem would take research , factory service repair information. Hooking up a professional type scanner or the factory tool ,checking for DTC'S - diagnostic trouble code's in all the modules on the vehicle ( 20) or so. Viewing data parameters on the scanner. With the complex electrical an electronics on your vehicle it could be a lot of different thing's .
Looking at wiring diagrams show's the complexity . free wiring diagrams here
http://www.bbbind.com/free_tsb.html Enter your vehicle info. Year , make , model an engine size. Under system click on lighting ,then under subsystem click on exterior lighting .Click the search button then the first blue link . View the diagrams an see if you can make heads or tail's of them.
A Controller Area Network (CAN Bus) is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other in applications without a host computer. It is a message-based protocol, designed originally for multiplex electrical wiring within automobiles, but is also used in many other contexts.
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How to Diagnose Controller Area Network CAN
