That sounds exactly my problem! Cheers for the advice. Will try again in the morning. Any idea which wire you plugged into? Hopefully get these fitted by the weekend .
As I said in my post in the previous page, I can't quite remember what colour the wire for the reverse light turned out to be in the end.
However, when I pulled away the trim on the right hand side of the boot, there were 5 wires going through the grommet. There were none on the left hand side - the wires on the left hand side when into the light cluster and not the grommet.
The 5 wires on the right hand side were as follows: 2 black wires - earths for the reverse and fog lights, one orange which I couldn't identify, one green and yellow which was the live wire for the for light, and then another wire with two colours on it - for me, this was the reverse light live, which is what you want to tap into for the parking sensors. I'm sorry I can't remember the colour of it, but by elimination, you know it's that one. The Haynes manual says it should be green and orange, but for me, it wasn't that colour either.
It is definitely one of those wires though. I tried the green and yellow one first, but my sensors only worked with the fog light on, so I took it off that wire, taped it with some electrical tape, and tried the other two-coloured wire, and hey presto, it worked.
Unfortunately you still need to use the Earth point on the LEFT hand side of the boot beneath the trim (the same one as in Preee's guide). But my wires for the sensor were long enough to use the Earth on the left hand side and the live wire for the reverse light on the right hand side. I just housed the buzzer beneath the trim at the mouth of the boot space.
However, you could feasibly just tap into the live wire JUST as it comes out of the reverse light behind the bumper. Up to you really.
Mine is also a Ghia 1.6 from 2006, so chances are we have some sort of unique set up for some reason.