Recommended 7-Way Trailer Wiring On 2007 Ford E-350 Super If you don't already have a 4-way wiring harness, we need to start there to get your 7-way. For a 4-way, I recommend the Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # C56020 which plugs in behind the tail lights of your 2007 E350. You will have to remove the tail light assemblies and interior trim paneling to access the factory connections.4.9/5(1) 2007 Ford E350 Super Duty Trailer Wiring And Electrical Equip cars, trucks & SUVs with 2007 Ford E350 Super Duty Trailer Wiring And Electrical from AutoZone. Get Yours Today! We have the best products at the right price.