Backup lights keeps blowing fuse

[MPAZ]

Hi to all
I mm new here.  I have a 2008 Gti and I know nothing about it.
A friend of mine left the car to me when he passed

My problem is that when I put the car into reverse it blows the fuse
I think there is a direct short in the wiring but
Don't know where to begin trying. To find it
  The car had a lot of rat damage to the wiring which has be repaired.
I know that there a a large number of
Items also powered on the same circuit.
Where would and how would I begin to check
Things out.
Thank you
Mike

[lazy]

Does the fuse blow as soon as the ignition is switched on or only when reverse is selected. If only when reverse is selected unplug the reverse light switch off the gearbox, put a piece of wire, split pin or a paper clip between the two terminals in the plug, the reverse light should come on and if the fuse doesn't blow the reverse light switch is faulty. If the fuse does blow you need to check the wiring from the light going to the front of the car, through the boot lid.
Good luck hopefully it's easy to find the fault.

[MPAZ]

Thank you for the reply.
I have been looking at the problem and I was wrong
  The fuse blows as soon as I put a new one in
  I disconnected the backup lights at the switch and the same thing happens.
I have checked the wire on the hood for the windshield and that is OK.
I I don't have a wireing sematic so I am now at a loss. Don't know what to check next.i would like to purchase a factory service manual but as now have not been able to find one.  I don'tknow where to go from here
Thank you