duetto internal lighting circuit

Hi there I need more help!!! 

The lighting circuit in the van... the rear and right hand side (looking forward)  of the van the lights are working, strip lights and reading spot light.  The left and the bathroom are not working.

The voltage on the right hand spot light is 10 volts that drops to 1 on the left.... so I am assuming the cable's run from rear left through the center and right of van then over to the right and that this point the wiring has broken or something ....but I cant seem to be able to find the routing of the cable to establish the issue.

So question does anyone have any ideas of the wiring routing and does may assumption seem correct ?

Thanks