the speed sensor wire on rear left, and the speed sensor and the brake sensor wires on the rear right are going to the cabin through grommets in the side of the wheelwells and join the huge cable harnesses on each side of the car... they do not go through the spare wheel cavity. the cables in the spare wheel cavity are the power cables from the battery, and the cables for the air suspension, along with the trailer hitch, PDC, TV module wiring coming from the battery compartment and the radio wires if so equipped...

the extra weight that you put on to the rear axle may trigger some load sensors on the back that are acting up...

do you have xenon lights from the factory? do those lights go up and down on cold start-up? do the they point down all the times?