I gotta say, having done this job once, and finding it so repulsive, I would never reuse a switch that was funky in any way. The cost of a new switch, which is ridiculously high, is still worth it to avoid doing the job ever again. Having said that, my brand-new switch started throwing a code preventing me from using the cruise control, even though the brake lights are fine. I have been putting off doing the job again for a year. I hardly ever use the cruise, so I don't really mss it, but the damn dashboard message irritates the life out of me - every day.

 

My wife and I have done the brake pedal switch assembly replacement job on her 2006 XK8 twice. The first time was in October 2012, and we installed a brand-new assembly obtained from Jaguar ($125 at the time). I stored the original factory assembly on my garage shelf. When the new assembly began to get flaky in November 2016, I did not want to go to the trouble of installing yet another new Jaguar assembly in the car for it to eventually fail again. So I asked an EE friend to take the original factory assembly I had kept and repair it with much better-quality microswitches and much better-quality soldering. He did so, returned it to me, and my wife and I went through the torture of the installation process once again (she much more than me because she is the one who must work upside-down underneath the dash since my shoulders and hands are much too large to get in there). That refurbished assembly continues to perform perfectly today. I am betting that if you rebuild these assemblies with better components and better soldering, their failure rate will decline substantially....

 

Hello Jon:
I also teamed with my wife, only in reverse with me under the dash. I did do a test run yesterday to give the brake/cruise switches a workout in various modes but I could not get any faults whatsoever.
Similar to Fmertz post, I am thinking that the computer would throw an error warning if it was reading both "cruise on" and "brake light on" for more than just a short period of time (say maybe less than 1 second of which "feathering" the brake pedal could have produced before I adjusted the micro switch lever).
Regardless, I do have new 5 amp micro switches on hand if my current method fails so that I can refurbish the assembly.

 

That brake switch is a bit more tricky than it looks. There are those 2 switches, and then there is the adjustment of the trigger itself (a ratcheting sliding adjustment). All of this has to work together. As a general statement, best is to get a new part when the old one fails, then keep the old part and repair it as a spare. The switches have been identified before (pretty generic models) and can be soldered on the small circuit board with somewhat basic soldering skills. I agree that these switches should trigger together as much as practical, but none of us know the "code" in the control module doing the "validation". Could be a single occurrence or multiple occurrences over several trips with a reset.