10' Modular Plug-N-Play Wire Harness When you need an easy solution to install your lighted headache rack, our 10′ Modular Plug-N-Play Wire Harness is designed for an easy install. The 10’ wire harness runs under the bed, connecting to your 7-way trailer light connector, providing a pass-through, so you don’t lose the use of your 7-way plug. How to Wire Lights to your Truck Rack Jul 08, 2019Step 4: Attach Headache Rack Wire Harness. Now you will have to run the wire harness to the front of the truck where it can be attached to the headache rack. You will likely have to run the wiring over or around various components of your truck, including spare tires, exhaust, transfer cases, and more. Make sure the wiring is safe and is not located near any moving or potentially hot parts.