under the clock sounds like the system sentry. That crazy option that about 5 xj's ever had that monitors everything.
I can tell you this, my friends BMW had pad wear sensors, once they were tripped you had to replace the sensors, as the rotor actually wore through them to set the light.
They weren't expensive, about 8 bucks, and were located in a notch in the pad. Did you see anything similar to that?