I would like to fit a towbar. I know I will have to cut a slot out of the rear bumper, but are there any problems to connect the electrics?

Can I just connect the trailer wiring in parallel with the car's wiring? Are the wires heavy enough to carry the extra current? Will this upset the system? - as far as I know I have no warning of failed light bulbs on this car.

Also, does anyone know the best place to access the rear light wiring in my car in orer to connect to it?