Towbar
I've done it and it is not that difficult. If you buy a new towbar, you will get an instruction manual.
I bought an used towbar from a scrapyard! I got all bits and pieces except two brackets whisch is fitted in a kind of channel, so I had to make them my selves.
The wiring is only to connect the different wires from the towbar to the wires to the rear lights. I used Haynes Manual wiring diagram for that.
Check out the following websites (do a search). I found instructionmanuals there which gives an indication of what is needed. Bear in mind that there is different solutions how different brands og towbar is fitted.
BOSAL
BRINK