As an amateur mechanic, I often run into electrical issues when working on cars. Tracing down and repairing faulty wiring can be frustrating, but these common problems usually stem from just a few root causes. With some basic diagnostic steps and tools, you can track down and fix most automotive electrical gremlins yourself.
Conducting a Systematic Inspection of the Wiring
The first step in diagnosing any electrical issue is to thoroughly inspect the wiring harness. Look for:
- Exposed or damaged insulation - Bare wires can short circuit and blown fuses are a good indication of a short somewhere
- Brittle, cracked, or melted insulation and connectors - This points to wires carrying too much current
- Corroded terminals - Cause high resistance and voltage drops
- Loose connectors and terminals - Intermittent faults and high resistance
- Signs of rodents chewing through wires - An all too common problem
Inspect the harness routing looking for:
- Wires rubbing against sharp edges - Can wear away insulation over time
- Pinches, kinks, or splices in the wiring - Can break conductor strands leading to high resistance
- Areas that move excessively - Flexing wires will eventually break
Testing Connections with a Multimeter
An inexpensive multimeter is the most useful tool for diagnosing electrical faults. Set to ohms mode, it can measure resistance in circults and connections.
- Probe suspect connectors and junctions along the harness - Look forHIGH resistance indicating corrosion or loose fit
- Backprobe terminals at ECU connectors - High resistance means a bad connection
- Check continuity along lengths of wire - Open circuits point to breaks somewhere
The multimeter can also be used to isolate shorts by determining if a blown fuse is due to a short to power or ground.
Choosing Where to Start Hunting for Issues
In general, start diagnosis at one end of the affected circuit and work methodically towards the other end. However, a strategic approach can often zero in on the likely fault location faster:
- Multiple inoperable systems - Start at ECU connections and main power feeds
- Intermittent faults - Most likely a loose connector or short caused by wiring damage
- Blown fuses - Suggests a short somewhere in devices fed by the fuse
- Voltage drops - High resistance somewhere causes voltage to "bleed off". Move from battery towards affected component
- Open circuits - Start diagnosis between the failed device and the power source
Common Wiring Repairs and Solutions
Here are some typical DIY wiring repairs you can tackle:
Fraying Wires
- Carefully wrap compromised sections with electrical tape as a temporary repair
- For a more robust fix, slide heat shrink tubing over the wire, heat to shrink it down, then apply tape over that
Broken Wires
- Locate the break and splice in a section of similar gauge replacement wire using butt connectors
- Cover splices with heat shrink tubing for protection and insulation
Loose or Corroded Connectors
- Remove connectors and use small wire brushes to clean away corrosion on terminals
- Coat cleaned terminals with dielectric grease to prevent future corrosion
- Ensure connectors mate securely with a positive click when re-inserted
Rodent Damaged Wires
- Completely replace chewed through sections of harness with new wiring
- Wrap sections prone to rodent damage with wire mesh loom as added protection
With methodical troubleshooting and a few key tools, you can repair many common automotive electrical issues yourself. Knowing the right techniques will save you time, money and frustration.