Do not splice as there is no need to if the wire is good to the bad old plug, or if you have any extra cord. Do like habitat guy said and take the old wires off one at a time, then slide the new housing on and rewire the new plug one at a time. If you don't have a chart just write down the colors to the position and do the same on the new plug. Be careful as the trailer hot supply is hot all the time on most, but not all rigs. If you ground it accidentally you will blow a fuse or breaker. Good luck!