Hopkins 50918 Tow Doctor Vehicle Wire Harness Test Unit Designed so that one person can make sure a vehicle wiring harness has been installed properly and all functions are working Tests all tow vehicle functions - ground, brake, direction, backup, and auxiliary power Heavy duty 20 foot extension cord is included Saves time and the cost of a second person at the rear of the vehicle Adapts to 4 wire flat, 6 pole round, and 7 RV blade (7 way pin type available, model number 50944)