Christian P. Koop
For the benefit of those who are not familiar with or have not read the first two parts of this series, I will explain the main reason behind these articles.
History has a way of repeating itself, even when it comes to emergency response vehicle (ERV) maintenance and repair. I have seen many similar issues occur time and time again, and I feel sharing some of the problems I have encountered over the years may help some readers find solutions to issues they may currently or in the future encounter with their fleets.
Some of these fleet defects may have been created because of poor specifications that did not take into account real-world drive cycles, terrain, climate, vehicle weight, or a host of other factors that can affect ERV drivability, durability, and reliability-which in our business can mean the difference between life and death. Some of these issues are easily, or luckily as the case may be, discovered during the acceptance phase for a new fleet. Yet others are from manufacturing or component defects that appear after the units are placed in service. Some may not show up until the units have been in use for considerable time and may take many thousands of miles, hundreds of hours, and many months before they appear. Unfortunately, some of these issues can be very tough to deal with, and finding solutions for them can become paramount for all those involved in the process.
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This example shows burned insulation from the harness of a transmission
output speed sensor. (Photo courtesy of Gable Jean-Simon.)
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Low-Voltage Systems
One area I feel is a major source of ERV downtime and problems that can be very time consuming for technicians to pinpoint is the low-voltage electrical system. Although there have been many improvements in technology over the years with the use of electronics to control engines, transmissions, multiplex systems, electronic pump governors, wireless system components, and a host of others, an incorrectly designed or built low-voltage wiring system can lead to problems in these modern and sophisticated systems that can be chronic and difficult to find and correct-even for experienced technicians.
Over the years, I have seen problems that include incorrectly sized wiring that could not handle a load, poorly crimped connectors that increased resistance and created voltage drops, failure to have a drip loop or a service loop, incorrectly designed or mounted components that would fill with water and fail, and wiring that did not conform to specifications. I will provide some background and examples of the issues caused by these shortcomings and failure to follow important build requirements and procedures in the low-voltage electrical system.
Wire Insulation
For a number of years, both National Fire Protection Association (NFPA) 1901, Standard for Automotive Fire Apparatus, and the old ambulance standard, KKK-1846-G, which is being replaced by NFPA 1917, Standard for Automotive Ambulances, have required low-voltage wiring that is resistant to heat, abrasion, and chemicals. Basically what this means is that the material used to insulate the copper wiring or conductors must withstand a lot more heat and physical abrasion than the more common polyvinyl chloride (PVC) insulated wire you may find at your local auto parts or hardware store. The wiring must withstand the high under-hood temperatures found in modern automobiles and trucks and is also resistant to chemical degradation from gasoline, diesel, lubricants, coolants, and other fluids that would ordinarily damage lesser materials used for wire insulation.
This wire type is also commonly referred to as cross-