WARNING: This page is about a different car, the 2017 Jaguar XJ, 2016 Jaguar XJ, 2015 Jaguar XJ, 2014 Jaguar XJ, and 2013 Jaguar XJ. However, it is still accessible from the selected car via links, so may be relevant.
The stop/start switch is installed in the instrument panel and connected to the CJB via hardwired connection. When the switch is operated two signal lines from the CJB are connected to ground.