How to Rewire Your 20 Year Old Car and Save Thousands

Introduction

Rewiring an older car can seem daunting, but it is very doable for the DIY mechanic and can save thousands of dollars in labor costs. With some basic tools, patience, and by following proper safety procedures, I was able to completely rewire my 20 year old Honda and give it new life. In this guide, I'll walk through the whole process step-by-step.

Reasons to Rewire an Older Vehicle

There are several good reasons to rewire an older car:

• Restore functionality - Over time, wiring harnesses can degrade, causing shorts, loss of signals, and electrical gremlins. Replacing old wiring restores all electrical functions.
• Safety - Old brittle insulation can expose bare wires, creating fire hazards. New wiring eliminates this risk.
• Improve performance - Upgraded thicker gauge wiring allows for higher amp loads, supporting upgrades like high-powered stereo systems.
• Value - A rewired car can add value and appeal to potential buyers.
• Save money - Dealers can charge $1000 or more for rewiring. DIY costs a fraction of that.

Preparation

Successful wiring jobs start with good preparation:

• Create a plan - Sketch out a wiring diagram to understand all circuits and plan the new harness.
• Gather tools & supplies - Essentials are crimpers, wire strippers, connectors, electrical tape, wire, conduit, and a voltage meter.
• Take precautions - Disconnect the battery! Wear eye protection and work gloves for safety.
• Label wires - Individually label wires as you remove them to trace circuits later.

Removing the Old Wiring

With the battery disconnected, I started removing the old wiring:

• Take photos - Photos of the harness before removal helps for reference later.
• Remove panels - Take out any panels, seats, trim pieces to access all wiring.
• Unbolt harness - Unscrew or clip any bolts or plastic fasteners securing the harness.
• Pull it out - Carefully remove the entire harness, labeling each wire.

Building the New Wiring Harness

The most time consuming but important step is constructing the new harness:

• Follow the diagram - Refer to your wiring diagram to guide how circuits should be recreated.
• Cut wires - Measure and cut new wires to correct lengths for each run. Leave extra length.
• Add connectors - Crimp on appropriate connectors to wire ends. Soldering makes connections more robust.
• Organize wires - Bundle wires neatly together with electrical tape, wrapping groups into circuits.
• Protect wires - Enclose bundles in split wire loom or conduit for abrasion protection.
• Label everything - Using printed labels or heat shrink, identify all wires and connectors.

Installing the New Wiring Harness

Once construction is complete, I installed the new harness:

• Mount components - Bolt down fuse boxes, relays, and modules in original locations.
• Fish wires - Feed wire bundles through holes and conduits to each place needed.
• Attach connectors - Plug wires into devices like sensors, ECUs, and control units.
• Secure wires - Use zip ties and anchor points to neatly secure harness.
• Check connections - Verify wires reach and nothing is loose, frayed, or unplugged.

Testing and Verifying Circuits

With the harness fully installed, thorough testing is key:

• Inspect wires - Closely look over all wires and connections for any issues.
• Connect battery - Reconnect battery power. Do NOT start car yet.
• Check fuses - Verify all circuits have good fuses before proceeding.
• Switch ignition - Turn the key to test power and signal circuits are live.
• Start engine - Finally, attempt to start the car to confirm all works.

Troubleshooting Problems

If issues come up, here is how to troubleshoot:

• Consult diagram - Check the wiring diagram to understand the problematic circuit.
• Visual inspection - Look for loose plugs, bad grounds, bare wires shorting, etc.
• Meter test - Use a multimeter to test power and continuity in each wire segment.
• Compare both harnesses - Use the labels from original harness to compare and isolate issue.
• Research errors - Consult car forums and guides specific to your vehicle for known wiring faults.

Conclusion

While rewiring an older car is very involved, it is a manageable project for any motivated DIYer. The job requires methodical planning, patience during construction, diligent testing, and attention to safety. But it could save you thousands in shop fees while adding tremendous value and life to your vehicle. With research and care, you can handle this project!