Process: Investigative Considerations

It is advised that fuses be inspected during the course of most automotive fire investigations. This requires locating the fuses, which can be challenging in some vehicles. It is not uncommon for fuses to be located in more than one location – fuseboxes are usually found in the engine compartment and/or interior. In-line fuses may be located anywhere in the vehicle. Fusible links can be particularly difficult to find, especially after a fire. Access to a shop manual (or even the owner’s manual) for the vehicle will help the investigator learn fuse locations, intended current ratings, and the circuits controlled by each fuse.

Fuses should be inspected to determine if they have the correct current rating for the circuit and if they are open or intact. Obviously, severe heat damage from fire may melt the fusible elements and preclude any meaningful interpretation of fire cause. Also, short circuiting often occurs during a fire, so caution in the interpretation of blown fuses must be exercised. Nevertheless, fuse condition can give clues as to the fire origin or cause and it can sometimes help the investigator determine the time history of electrical power on the vehicle as the fire progressed. For example, for an advanced fire, a lack of blown fuses could indicate that system power was interrupted before the fire progressed very far.

Aftermarket wiring is always suspect (due to uncertain quality control) and should be carefully inspected. Wiring associated with sound systems, alarms, remote starters, engine block heaters, and other add-on accessories may not be correctly fused, and may not be properly insulated or protected from unwanted electrical contact or abrasion. It is also possible that factory wiring may be damaged by installation of other accessories when holes are drilled in the vehicle or sharp screws penetrate the insulation of a harness.