I've seen elsewhere on the forum that the answer to this question is - the switch on the gear box.... But I don't get it! The reversing light doesn't shine. I've replaced the bulb again and again. Checked the fusebox - all fine. Got hte multimeter out and when the car's in reverse, there's 12V into the bulb socket but as soon as the bulb is fitted the 12V disappears. When the live contact is depressed using a plastic peg, the 12V continues to flow but if you use the bulb itself, the power to the socket is cut... How is that the fault of the switch on the gear box?

[quote name='sail2bob' timestamp='1313425449' post='140137']
I've seen elsewhere on the forum that the answer to this question is - the switch on the gear box.... But I don't get it! The reversing light doesn't shine. I've replaced the bulb again and again. Checked the fusebox - all fine. Got hte multimeter out and when the car's in reverse, there's 12V into the bulb socket but as soon as the bulb is fitted the 12V disappears. When the live contact is depressed using a plastic peg, the 12V continues to flow but if you use the bulb itself, the power to the socket is cut... How is that the fault of the switch on the gear box?
[/quote]

Could well be down to current and resistance, there is a standard flow there when you press the plastic peg, there is still no resistance on the line, however as soon as you insert a bulb the resistance increases, the switch could be failing because its detecting too much resistance?