Others will know more about putting one in, but I think I read somewhere that the connections and wires are there already. If they are, just swap the trip computer in and you're set to go. You will also need a temp sensor for under (on) the hood. I think you'll have the connector for that there too.
Depending on the year of your truck, the fuel mileage and odometers won't function. Newer 24V trucks have all the features available.