The light in the boot of my 550 '98 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? Thanks, Antonio
Mistery solved! It turns out that there is a switch. Quite hidden under the molded part screwed to the boot door. 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 no need to turn the ignition key on. The positive 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.
