The i3, like probably all BMW's and many other cars these days, rely in the serial CANBUS to tell things to turn on and off. FOr example, on my ICE, the rear light assembly has: brake, running, turn, fog lights and only 3-wires going to it. Now, you cannot individually control four things with only three wires without some 'magic' going on. If you've ever looked at some of the switches in a BMW, you'd find that they are usually microswitches, and definitely aren't designed to support actually switching power to things...they send a signal to the computer, and it then talks to a driver closer to the device. On my ICE, when a trailer is attached, it does numerous things: turns off the US sensors in the rear, changes the rear camera view to make it easier to line up with the trailer, modifies the stability control logic to account for the trailer being there, and last, but not least, controls the trailer lights, and if it needs to, its brakes. I doubt the i3 has the corporate logic to accept a trailer logic module, and that means, if you were to do one with lights, you'd need a passive CANBUS system to listen and then drive the trailer's lights as required. To ensure that at least the brakes and emergency flashers work, in addition to connecting to the CANBUS, the device I have for my ICE, also connects to the center brake light and the right-hand turn signal...when the car is off, it sees the center brake light, and will activate the brakes on the trailer. Same thing, it sees that the car is off, and the right-hand blinker is on, then turns on the flashers. When the car is on, and the CANBUS is properly functioning, it ignores that emergency logic. If you just try to tap into the lights to power the trailer, you'll probably cause the car to at the minimum, issue warnings about the lights, and at the worst, fry something.