Pinched wires

About eight years ago, I worked on a brand-new heavy-duty wrecker that had just come back from the factory where they had installed the bed on the chassis.  When the turn signals were activated, the rotating beacon lights would start turning and stop turning, start and stop, at about the time interval that the turn signal lights would normally flash on and off.  After going over the entire chassis from front to back, I found a section of heavy-jacketed electrical cable between the outboard face of the driver's side chassis frame rail and a toolbox mounting bracket.  Someone at the factory had installed the toolbox mounting bracket on the chassis and failed to notice that the electrical cable was hanging between it and the chassis.  The act of tightening the toolbox mounting bolts with a large impact wrench pinched the cable between the toolbox mount and the chassis frame and shorted the wires together inside the cable.

Wires run too tight

Electrical wires run too tight around corners of the bed cause short circuits.  I'm convinced this problem comes about when people assembling equipment at the dealer or at the factory do not realize how much over-the-road equipment flexes and moves.  Any equipment that goes over the highway, especially equipment made of steel, tends to flex a lot more than most people realize, and if you work as I do in a shop environment where all equipment that comes into the shop is unloaded and at rest, it's easy to underestimate the potential for movement to tighten and chafe wires.  The inelastic nature of copper-stranded electrical wire also contributes to the problem.  Solve the problem by installing a little extra length in the wires around every corner or bulkhead.

Mis-measured installation

My favorite assembly error is mis-measured installation, which can always be relied upon to produce comical results.  I remember years ago seeing a brand-new rollback in the install shop of a wrecker dealer.  The technicians had just finished building the truck, and they went to roll the deck forward and give the truck to the buyer.  When they rolled the deck forward, the deck went right through the back of the cab.

When you take delivery of new equipment, head off assembly errors before they cause problems by checking the lights, operating all the hydraulics, and looking under the truck.  Have someone else operate the bed and the lights while you watch from the back.  Plug in the tow lights.  Be exhaustive.  Remember that shiny wheel simulators and fancy paint schemes don't necessarily mean the wiring and hydraulics have been installed properly.