jackrae:
In most older car designs the boot switch is actually a grounding device. ie the lamp is permanently supplied with a 12 volt line and the other side of the lamp then runs to the boot switch. When the boot is opened the switch actually takes this line down to the chassis of the car, so completing the circuit to the lamp. ie a "grounding " switchSo the first question you need to answer is " Does the switch have 1 or 2 terminals"
If only 1 then you have a "grounding" switch. If so then I suggest that there are at least 5 possible options
a) the 12 volts line to the lamp is defective
b) the lamp holder connections are corroded
c) the lamp is dead
d) the wire from the lamp to the switch is defective
e) the switch is defective (possibly just corroded)You have not advised the model or age of the car --all information that might get you an informative answer
The car is a Toyota Avensis T22 from 2002. I cannot check the resistance or anything of the switch because it is not easily accessible. It is burried under the trunk latch...