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asalcedo · 06:37 PM

Mistery solved!

It turns out that there is a switch. Quite hidden under some molded parts. It consists of a metal ball that closes the circuit when the boot door is fully open.

The ball was not making contact with the cable terminals. I replaced the terminals and got the switch working fine.

There was indeed no need to turn the ignition key on. The positive battery pole is always connected to the bulb holder. It is the negative pole the one that is switched by the ball. Thus, there is always 12V between the positive pole at the bulb holder and any metal part in the car, which is connected to the negative pole of the battery.

Quote:

Originally Posted by Andrew Gabriel

In article ,
Harry Bloomfield writes:
Matty F wrote :
I took the bulb holder apart and found a mercury switch inside. The
mercury was coated in oxide. I took the mercury out and cleaned it and
cleaned its container. The switch worked perfectly after that.

A mercury switch - that would make it a very long time ago :-)

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.

--
Andrew Gabriel
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