How to Rewire Your 20 Year Old Car and Avoid Costly Repairs

Introduction

Replacing the aging wiring in your 20 year old car can dramatically improve reliability and avoid expensive electrical issues down the road. Rewiring a car may sound daunting, but with some planning, basic tools, and perseverance, it can be a manageable project. Here's how I successfully rewired my 1996 Honda Civic to keep it running for years to come.

Things You'll Need

Before starting, make sure you have the necessary supplies:

• Wiring diagram for your specific make and model. This is essential for knowing wire routing.
• Automotive wire in various gauges. I used 16, 14, and 12 AWG for different circuits.
• Crimp connectors and heat shrink tubing to connect wires.
• Cable sleeves to protect and organize wire bundles.
• Electrical tape for temporary connections and wire labeling.
• Wire stripper and crimper tools.
• Voltmeter to test connections.
• Zip ties and clips to secure new wiring.

Planning the Rewire

Careful planning makes the rewiring process smoother:

• Work from a wiring diagram to plan which circuits to replace. Focus on the oldest, most critical wiring first.
• Label each wire with tape as you remove it to identify where it routes.
• Plan where wiring harnesses will run and how to secure them. Inside trim panels works well.
• Determine the length of replacement wires by measuring old ones. Leave some extra length.
• Keep a notebook to document each circuit as you work.

Removing Old Wiring

Taking out the existing wiring is the first step:

• Disconnect the negative battery terminal. This disables the electrical system while you work.
• Remove interior trim pieces to access wiring routing paths. Be careful not to break plastic clips.
• Locate connection points for each harness and unplug or cut them.
• Carefully pull harnesses out of their routing paths. Use tape labels to track them.
• Inspect connectors and terminals. Clean or replace corroded ones.

Installing New Wiring

Now you're ready to run new wires:

• Begin with the hardest, most buried cables first. Leave accessible ones for last.
• Route wires into trim panels or under carpeting, following the factory paths.
• Wrap bundles together with cable sleeve for organization and protection.
• Use grommets when passing through metal to avoid wire damage.
• Make connections with crimp terminals and heat shrink. Solder if desired for longevity.
• Confirm wires reach their termination points without pulling or stress.

Reconnecting Circuits

The final step is hooking up all the new wiring:

• Reconnect negative battery cable to re-energize the electrical system.
• Plug in connector blocks on each new harness one-by-one.
• Verify operation of electrical circuits as you go. Check lights, signals, gauges, etc.
• Test for shorts or faults by checking circuits with a voltmeter.
• Seal wire entry holes with silicone once everything is working.
• Secure wiring with zip ties and clips to prevent rattling.
• Replace trim panels and reconnect battery when complete.

Testing and Troubleshooting

Be methodical when testing and fix any issues:

• Check circuit voltages to confirm power and ground connections.
• Wiggle test wiring to identify shorts.
• Inspect connections closely if something doesn't work. Redo if needed.
• Consult wiring diagrams to confirm routing and connector pins are correct.
• Check fuses. Overlooked blown fuses can cause problems.

With attention to detail and by systematically working through each circuit, you can avoid headaches and be confident your rewiring job will last for years before the next overhaul is needed. Take your time and be thorough for best results.