I installed a draw tite and the wiring module a year or so ago. I ran my batt+ wire underneath the car then upe the firewall and routed it through the engine compartment to an inline fuse and then to the battery positive. (I don't trust the excessively tiny wires Volvo uses for things like the cigarette lighter for powering lights or anything.) I also placed the module in the lower left rear panel directly behind the rear wheel and routed the wiring out through the drain port for that area. It was easy to "tap" the tail/stop/turn signal wiring from this areal and this keeps the module dry and relatively cool.

Running the wire to battery takes some patience and a lot of wire ties. I also encased my wire in PVC wiring loom since there is a lot of hot exhaust and mufflers etc underneath. You can also run it through a factory wiring protector for a while about midway up the car. I've not had any problems with it in a year so far.

Good luck.

M