Introduction
We've all been there - that one electrical issue in your car that just won't go away no matter how many times you take it to the mechanic. The radio starts cutting out, some dashboard lights flicker randomly, or maybe the power windows stop working every few weeks. The problems seem to come and go, and the mechanics can never recreate the issue when you bring it in. Tracking down an intermittent electrical gremlin can be incredibly frustrating and time consuming. But with some diligence and testing, you can hunt down even the most elusive electrical faults. In this guide, I'll walk you through the systematic process I use to diagnose difficult electrical issues that no mechanic can seem to locate.
Start With The Basics - Inspect Connections and Components
The first step is to thoroughly inspect the electrical connections and components that could be involved with the faulty system. Look for any loose, damaged, or corroded wiring and connectors. Issues like loose battery cables, damaged ground straps, or corroded plugs can cause all sorts of weird electrical glitches. Carefully follow each wire and use a multimeter to check for continuity or drops in voltage. Replace any components that look questionable. Sometimes simply re-seating connectors or replacing a shoddy ground strap is all it takes to fix a stubborn electrical gremlin.
I once spent a whole weekend chasing an electrical fault in my truck that would cause the interior lights to cut out intermittently. After tearing apart the dash and testing wires for hours, I found the problem - the main ground cable connection at the battery was loose. The cable looked fine, but the clamp was just slightly corroded. I cleaned it up, tightened the connection and the problem was solved! Always check the simple stuff first.
Use a Multimeter to Diagnigate Voltage Drops
The next step is to break out the multimeter and start testing circuits for unwanted drops in voltage. Set the multimeter to DC Volts and probe connectors or wires for power and ground at both ends of a circuit. If you see more than a 0.1 Volt drop between points, you have located a source of excessive resistance in the wiring.
For example, if you are chasing an ignition or fuel issue, probe the positive and negative terminals on the coil pack. Then, probe the power and ground wires where they connect to the vehicle's wiring harness. If you see 12V at the coil but 11.7V from the harness connection, you have found a 0.3 Volt drop in that circuit. That points to a possible faulty wiring connection.
Tracing and quantifying voltage drops allows you to isolate the exact location of the fault. The mechanic can then focus on repairing or replacing that wiring section rather than guessing about the problem.
Log Problems and Symptoms
Intermittent faults can be incredibly difficult to diagnose because they seem to occur randomly. The key is to closely log exactly what was occurring when the fault happens. Note details like:
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Environmental conditions - Temperature, humidity, etc.
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Operating conditions - RPM, electrical load, engine load, etc.
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Duration and frequency - How long does it last? How often does it occur?
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Associated symptoms - Any other things happening simultaneously?
Look for patterns that link the fault to certain conditions. For example, does the radio cut out most often on cold days or when hitting bumps? That points to a temperature or vibration sensitive issue. Logging this data helps narrow down the list of suspect components.
Use a Wiring Diagram
An automotive wiring diagram allows you to see how different systems and components interconnect. When chasing an electrical fault, consult the wiring diagram to identify all devices involved in that circuit. Then, use your multimeter to test wires and connections at various points along the path. The diagram combined with voltage drop testing will help you close in on the shorted or damaged wires.
For example, if the power windows are acting up, consult the wiring schematic. You'll see the path electricity takes from the switches, through any control modules, relays or motors and back. You can then probe that whole circuit to isolate the drop in voltage indicating the source of the fault.
Consider an Intermittent Fault Diagnostic Tool
For extremely difficult to reproduce electrical gremlins, you may need to break out a specialized diagnostic tool. An intermittent fault detector allows you to monitor vehicle circuits long term in order to catch faults in the act.
Popular options are devices like the Power Probe or Amp Clamp that attach to wiring. You can set them to monitor voltage, resistance or amperage fluctuations over time. The device logs any electrical issues and alerts you the moment one occurs. This allows you to identify faults even if they are not happening when you are testing.
While pricier, these diagnostic tools can save lots of headaches when dealing with very tricky electrical bugs. Just be sure to research options compatible with your vehicle make and model.
Be Methodical and Patient
It can be frustrating chasing an electrical fault that seems to occur at random. But by following a thorough diagnostic process, you can get to the bottom of even the most troublesome electrical gremlins other mechanics struggle with. Start with the basics like wire integrity and connections. Follow up with voltage drop testing and logging symptom patterns. Consult wiring diagrams to open up possibilities. And consider specialized diagnostic tools to monitor electrical parameters over time. With persistence and diligence, you can hunt down that super annoying electrical issue once and for all.