asalcedo wrote:
The light in the boot of my car does not light up.

I have checked the bulb and it is fine.

I have checked the voltage at the bulb holder without the bulb and
with the ignition key turned on and it is 12V

However, when I put the bulb in the holder it does not light up and
the voltage is 0, even with the ignition key turned on.

Where is the fault?

First thoughts are grounding issues. Is the earth secure? Are both
connections to the battery clean and secure - this should be likely if the
car starts but you never know. Then I think we go into deeper issues
relating to the loom and then difficulties arise. Has the car suffered a
collision and then where? Any wiring connections in that zone?

Good luck.