mdooher: Not sure about Mazda, but on my vehicle (BMW) plugging in the trailer changes the behaviour of the stability control and alters the gearbox change steps etc. It also allows the trailer lights to be tested as part of the bulb test system.
If your vehicle is designed to do this then you need to find out if it uses a towing module and if it is fitted. Many BMW owners get an auto sparky to install a couple of relays to make the lights work...silly move
Likewise, Land Rovers have a small green trailer symbol that flashes in conjunction with the green left and right arrows to show that your trailer lights are working.
Also just as general info, Land Rover wire the cars for trailers in the factory so when they arrive in their delivery country, all they need is the appropriate tow ball and an adaptor to go from a UK round trailer plug to whatever the delivery market uses. The dealer told me that costs a buyer about $600 as opposed to the $3,000 to put one on an Audi Q7!


