This will probably be figured out tomorrow morning, but here goes.

I've been trying to install a reversing camera, powering its' trigger by using the centre pins of the lighting cluster. Messed up the wiring so disconnected it all ... so imagine the vehicle is back to how it was before. 

My fuel gauge has gone bananas, so contant 'low fuel' beeping. swinging from 0 miles to 70 miles of fuel left. Then engine management light stays on. Now the speedo is stuck at zero, and the odometer as  a result. Reverse sounder isn't working either.

Another thread has an entry referring to the reverse light sharing power with the speedo, etc- which kinda points the finger at me, fcking idiot. The route i took for the camera cabling ran from the rear hatch handle, up the passenger side of the hatch to the roof, and i took a power lead from the left rear light (centre pin) and ground from the bodywork along the passenger side. Sure I poked some wires when getting through the hatch cable shroud which goes to the roof, but its unlikely I punctured the insulation.

Any thoughts on how to go about resolving this, and have I possibly blown something along the way? how does it all go together?  And what's that bolt and wiring directly underneath the left rear light cluster?

Car is a VRS 2005

oops- odometer is ok, I meant the trip computer