Electrical problems can put emergency vehicles out of service as fast as flat tires. Technicians who follow some basic electrical troubleshooting procedures can often get these vehicles up and running with a minimum of time and expense.

Electrical troubleshooting is different than electrical maintenance. Maintenance usually involves inspection and adjustment of major electrical components such as batteries, alternators and starters to keep them operating properly. Troubleshooting, on the other hand, involves locating and fixing electrical problems once they occur. Sometimes these problems are difficult to find. Rather than starting at one end of a circuit and blindly testing or replacing each component, smart technicians often use a step-by-step approach that helps them quickly isolate the problems.

Although different vehicles can have different electrical problems, the basic troubleshooting procedures always involve the same five steps.

1] Understand the principles. Complex diagnostic tools do a lot of the work for you, but for simple electrical circuits, it’s important to understand the relation between volts, amps and ohms. Every component in a circuit has resistance (ohms). The biggest drop in potential (volts) should be across the component with the biggest resistance — that should be the load, such as a motor or light bulb. If another component has the biggest voltage drop, you have a problem. Likewise, every circuit should be flowing current (amps) through each component when the circuit is on. If there’s little or no current flowing through a component, you have a problem.

2] Review the problem. Analyzing the problem before you start work can often narrow down your search to a specific area of the electrical system. What component isn’t working? Is another component also not working? Check a wiring diagram to see if the two are related. Does the problem happen only under certain conditions? This can give you valuable clues, especially when dealing with intermittent problems. Has the problem happened before? Check the maintenance records of the vehicle, as well as those of any similar vehicle, to find out. Are there signs of damage in the area of the problem? Check for evidence of impacts or electrical arcing.

3] Get the necessary tools. Vehicle electrical systems are becoming more complex, and you need to have the proper diagnostic equipment and reference materials to locate problems. Diagnostic equipment may include hand-held circuit analyzers in addition to the more traditional test lights and volt-ohmmeters. Major components, such as engines and transmissions, may each require their own special diagnostic tools and procedures. Without these special tools, it's almost impossible to locate problems in those components. Reference materials may include wiring diagrams, part drawings, service manuals and troubleshooting guides. Some vehicle manufacturers provide this information in a printed manual, while others provide it on a compact disc or through the Internet.

4] Pick a starting point. Service manuals and troubleshooting guides for multiplex electrical systems and other complex electrical components may describe a specific starting point and specific procedures to be followed based on the symptoms of the problem. Read the manuals before you start. For circuits involving less complex components, you will need to pick a starting point somewhere in the area of the problem. When that's not possible, or when the symptoms don't clearly indicate the problem area, you should check an accessible point near the middle of the circuit. If the circuit checks out at that point, you know the problem is most likely farther on toward the ground. If the circuit doesn't check out at that point, you know the problem is probably farther back toward the batteries. Either way, you usually only have to check half the circuit.

5] Check for power, ground and continuity. All electrical circuits must have adequate power, a good ground and an unbroken conductor from one end to the other in order to work properly. If you use a special diagnostic tool to troubleshoot more complex circuits, the tool usually checks for power, ground, and continuity as part of its preprogrammed tests. If you are manually troubleshooting circuits involving less complex components, you will need to make the checks yourself. To do this, ask yourself some questions. What should I check and where should I place the test leads to make a valid reading at this point? Do I need to turn any switches on or off, or do I need to disconnect any components before I take a reading? If I do not get the reading I expected, what might be causing the discrepancy and what should I check next?

A logical, step-by-step electrical troubleshooting approach usually can locate problems more rapidly than a random, trial-and-error approach. It also is less likely to cause unnecessary and costly replacements of perfectly good components while you search for the problem. The next time you tackle an electrical problem, follow these five easy steps to a simpler, faster and more accurate solution.