Wiring harness concerns have been a part of automotive diagnostics since the beginning but cars and trucks are infinitely more complex now. Any technician can tell you that it goes with the territory. Ford trucks over the years have had their share of issues and over time we discover pattern failures and common areas where wiring faults tend to occur. On 2008 and newer Super Duty trucks one such area is located near the front left shock tower shown here. This is a location on the truck where a lot of the wiring is found because the battery junction box containing many of the fuses and relays for the vehicle is located there. Additionally this area of the truck is where many circuits pass through the firewall to the instrument panel. There are also several harnesses that continue down the left frame rail that contain circuits for many systems and components like the transmission, fuel system, exhaust aftertreatment systems, braking, and lighting to name a few. Any time you encounter faults that point to circuit faults pay close attention to the wiring in this area of the truck. In the pictures the inner wheel and splash shield have been removed to access the wiring for inspection and repairs.
To the right is a close-up of the typical wiring damage caused by chafing you will likely find. Chafing can occur on the shock tower, the brackets mounted to the shock tower, the splash shield and even within the harness itself. Let's take a closer look.
Point A This wire actually rubbed through on the edge of the plastic harness protective tubing. Wrapping the wires with electrical tape at the end and then to the protective tubing will prevent this from happening.
Point B This wire was rubbing on the edge of the splash shield. Additional wires were rubbing there as well. Securing the harness away from known chafe points and limiting movement will prevent this from happening.
Once the wire insulation is removed water and road salt cause the copper wire to corrode while continuing to chafe accelerating the failure. Repairing these circuits often requires cutting out a section of the circuit extending a few inches in either direction to eliminate corrosion that has spread inside of the insulation. Splicing in new wire and replacing the wire terminal at the hard shell connector is commonly required to make an effective long lasting repair. Always seal splices with adhesive lined heat shrink tubing that will prevent water from re-entering the wire causing repeat failures. When repairs are completed be sure to re-route and positively secure the harness away from the contact points that caused the failure in the first place.