Andrew Gabriel wrote:

Many years ago, my father had a Citroen GS which had a mercury
switch for the boot light. Being sealed, they are normally very
reliable. Sounds like Matty's one wasn't sealed.

With regards to more recent cars, I've had the both the light
switch fail high resistance due to dirt ingress, and the earthing
of the boot hatch go high resistance through its hinges (which
stopped the rear window heater and rear wiper from working).
In the latter case, I connected an explicit earth tail between
the hatch and the car bodywork, and that was still working fine
when I sold the car ~5 years later.


I'm not sure what Matty saw. Surely mercury would evaporate over enough
time? And I'm really not sure how you clean it. Kind of hard to polish
a liquid!

But only Citroen could put in a boot switch that makes the light come on
whenever you brake...

Andy