Join Date: Jul 2005
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If anything, number plate mounted sensors will be too low on the Lag 2 hatch, thanks to the number plate being on the bumper. I mounted the ones on my last L2 either side of the number plate, even though this was lower than the position given in the instructions. The result was that they'd give a 'long range' warning beep when there was nothing behind you, but they still got progressively faster and went to a constant beep as you reversed up to an obstacle, so they were perfectly useable.
If you really don't want to drill holes, then that may be your best option. I mounted the sensors either side of the number plate and ran the wires up through one of the number plate lights. Routing the wires was tricky without removing the bumper, but possible using a bent wire coathanger and removing one of the rear main light clusters.
A compromise would be to drill the sensors into the bumper rubbing strips (which is where the factory ones are located anyway on the hatch.) That way, you're only risking trashing a rubbing strip, rather than the whole bumper (though I expect the strips don't come cheap if you need to replace them either.)
Currently in Horatio's garage:
2010 Laguna III Initiale.