I agree with Dave you could be getting a "pig in a poke". You might be lucky enough to find a webpage of the manufacturer that will give you instructions. Otherwise if you do not know the history of it then I would think twice. I picked mine up for a little more than $100.00. If you do go used take time to test it good before starting out on a long trip. I almost had my 24' camper get away from me this summer, driving too fast and caught a groove in the road and started swaying, even with a sway bar, so I grabbed the brake controller to slow the trailer down which it did and it straightened right up. It was not a time when you hoped it would work, we all were a little tense for a few seconds.