This article provides background information that will help you troubleshoot most basic electrical problems. Included are some basic hints when trying to track down an electrical failure, whether it's your stereo, your air system, or your cigarette lighter- powered blender. Diagnosing electrical-system problems can seem very overwhelming at first, but if you break it down into the system's components, it becomes much easier. Some people just replace things until they eventually fix the faulty part. While there are times when this is the best way (to substitute a known good part), it can be costly, not to mention frustrating. Instead, use your money to purchase a quality volt-ohm meter that can read voltage, resistance (ohms), and continuity.

The most helpful tool you can have is a high-impedance volt-ohm meter (low-impedance Voltmeters will give misleading information and can damage sensitive electronics). An accurate wiring diagram will quicken the diagnosis process tremendously but is not always available, so we also included a wiring diagram of the issue we'll be troubleshooting in this tech piece. Whenever you're making electrical repairs or doing work on your truck, always disconnect the battery. Batteries can and do explode, so avoid creating sparks near the battery by turning all accessories and the key off before undoing the cables. The negative side should be the first thing undone and the last side reconnected.

Consider the electrical system on your vehicle as a collection of many smaller sub-systems that are capable of working independently of each other. Electrical circuits can be broken down into six simple components: power source, protection, control, load, ground, and wiring. The battery is considered the power source, protection is the fuse or circuit breaker, control is the switch, load is the component doing the work (compressor, headlights, coil, and so on), and a good ground completes the circuit. The wiring is what connects everything together. Remove any one component and the system will not work. Electrical diagnosis is a systematic method of identifying and correcting the problem component. The main problems you'll run into are open circuits, shorted circuits, excessive resistance, and faulty parts.

In this tech piece, we'll use some basic steps addressed to try to track down the possible reasons why our air compressor will not turn on. Always begin with the basics in any electrical system by checking for a fully charged battery; clean battery terminals; positive and negative cables with proper routing and clean, tight connections; and fuses that might be blown. Most electrical diagnoses are done with the battery hooked up and the system operating (you can't check the turn signals without first turning on the ignition switch and placing the turn signal lever either in the left or right position).

Open Circuits
Use your meter to make a quick check for continuity. Hook one lead of your meter to one side of the circuit and the other lead to the other side. If your meter has a sound function, it will beep to signify continuity. However, this will not be the case in an open-circuit situation. The current is not getting to the end source because of a break somewhere in the circuit. Turn the faulty circuit (your compressor) on and use your meter to check for voltage at various points. If you get a voltage reading of 12 or more, your circuit is probably good to that point. Check the ground or negative side of your load to make sure it's good. Most problems occur in the ground side of a circuit. The quickest test for an open ground is to run a known good ground wire (jumper wire). If your meter did not read voltage at the positive side of the load, then back up to the switch controlling the circuit (pressure switch). Your meter should read voltage when you probe both sides of the switch. If it doesn't read voltage yet, back up to the fuse block. If the entire circuit is getting the necessary voltage, then the problem is probably a faulty part.