Like said, just go to your local autoparts store. There's a plug in the back that can be simply T-eed into and the auto parts store will have the 'T'.<p>If you are putting on electric trailer brakes, then you will have to do a little more. Again, autoparts store would be best be for complete setup.
I have found the best place to get trailor wiring and hookup supplies is at your local RV center. If it is a simple hookup, such as a flat wire plug then an auto parts store or even K-Mart will have the supplies needed.