First thing is to chek your car is Type Approved for towing (not all are). Check the VIN plate on the B pillar and look for the towing weight. Assuming that's good then cross reference the part number against the manufactures website. If its detachable it's likely to be from Bosal/Oris, Westfalia, Witter or GDW. You then need to check if the car needs a bigger cooling fan. Merc (generally) only fit 450W fans, but cars leaving the factory with towbars have upgraded 600W fans. Electrics - make your life simplier by using a dedicated wiring kit. Bypass kits work but do not allow the full adaptablitity of the cars systems (such as traction control, air suspension) to towing. Coding can be done with anyone with access to bi-directional coding machine. A dealer would likely charge you an hours labour. I would internet search Mercedes Coding close to where you live an see what comes up. I am assuming you are going to fit this yourself (?) as most fitters will only fit new bars/electric for warranty/assurance purposes.