Number one, what brand of truck and how old? Most (about 2000 and newer) domestics and some imports have a plug under the dash that the wiring harness for the brake controller plugs into. Unfortunately those that don't means more work. If you don't have the trailer package, then you need to run at least one more wire from the front to rear 7 pin connector. Left/Right/Park/Trailer Brake/Ground. The other 2 are for reverse lights on trailer and one to charge the trailer battery, I don't use either of those two. Most of the brake controllers come with pretty explicit instructions, pay real close attention to the colour codes, white is negative, black is positive, blue is trailer brake and the other colour(usually red or red stripped) is the tow vehicle brake signal to turn the brake controller on. If you have to add wiring through the firewall, sometimes theres a rubber plug than can be knocked out or poked through to get the wiring through it and run it along the frame rails to the back. You can get rid of the rear 4 pin conector and run those wires into the 7 pin. If you ever need to use a 4 pin connector, there are adapters readily available. More questions, ask away. If you don't do it yourself, I would go to an RV place. They install enough of them to prevent problems that some have no idea what they're doing.