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HomeTips & GuidesHow To Rewire a Car — A Comprehensive Step-by-Step Guide

How To Rewire a Car — A Comprehensive Step-by-Step Guide

How To Rewire a Car? A car wiring harness system plays a critical role in ensuring the functionality of a vehicle. 

Unfortunately, most car owners often ignore this aspect when conducting their maintenance routine until it’s late. 

Undeniably, learning how to assess the wiring harnesses or at least know how to rewire is a long task that requires skills and patience. We will guide you through the entire process smoothly.

Create a wiring diagram.

Compared to the old days, nowadays, modern cars have more circuitry in their systems. Usually, you’ll need approximately 12 circuit harnesses for cars like Model A hot rod and T-bucket. The circuits may need accompaniments like a charging system, lights, horn, ignition, etc. 

Contrarily, vehicles with additional accessories like air conditioning, power windows, and audio systems will need up to 28 circuit harnesses to operate. 

An engineer mapping out wiring diagrams

 (An engineer mapping out wiring diagrams)

The first step in installing a harness is familiarizing oneself with the circuits and wires. Ensure you trace the wiring system and map out where every wire goes. 

Prepare tools

Wiring tools

Some of the tools you’ll need for the rewiring process are:

  1. Wire strippers: A quality set of these tools will help remove insulation from the car wires while sparing your wire conductors. 

Wire stripper or cutter

(Wire stripper or cutter)

  1. Soldering iron enables you to secure oversized connectors that you can’t crimp and splice wires. When buying the solder, ensure you get the type specifically designed for wiring and electronics. You’ll notice it by its mildly activated rosin core flux. The rosin material gets rid of light corrosion and oxidation. 
  2. Wire crimper: It is an instrument necessary for installing solderless connectors. Some come with wire stripping and cutting sections. But the ones in the market often have three or two sections on the nose that can suit different lug sizes. 
  3. Shrink tubing: For insulating connections from the external components, 
  4. Test light: It examines the power in the circuit.
  5. Ohm/Volt meter: It measures resistance and voltage levels in the circuit.
  6. Wire brush removes grease, oil, or heavy corrosion before you begin soldering. 

Specific parts

They include sections like tail lights, headlights, engine compartment, gauges, dash switches, etc. 

Wire types

The types of wires manufacturers produce depend on different vehicle applications. Therefore, choosing the right type to prevent accidents during the setup is important.

Some examples include:

  • Primary or General Purpose Thermoplastic (GPT) wires for interior applications.
  • Motor wire
  • Thin-wall cross-linked (TXL), SXL, and GXL wires
  • Battery cable
  • Speaker wire (for speakers)
  • Trailer wires

Protective measures

  • Vibration often damages wires. Moreover, when wires rub against each other, the internal copper strands may break or result in a short circuit. As such, ensure you secure all your wires to reduce mobility. 

Turn off the car’s power. 

Car start-stop system with finger pressing the button

(Car start-stop system with finger pressing the button)

First, you ensure safety by disconnecting all devices and turning off your car’s power. Then, loosen the car bolts from their nipples and subsequently remove them from their corresponding terminals. The process will automatically disengage the battery cables. 

Afterward, place the removed components in a secure place, ensuring they don’t get in contact with any exposed metal parts or with each other. 

Next, remove any extra wires that may still connect to the battery’s terminals. Then, use an insulating tape to cover them and stow them away. 

Cut the main wiring harness.

We want to find the main wiring harness in your car’s engine bay. Normally, every wiring harness has its rubber grommet routing. 

After locating the harness, cut in midway between the entry to your cabin and the engine bay. Next, draw out all old wires from each side of the grommets. Take extra care not to cut any of the remaining wires. 

Then, use a multi-way crimping tool to strip each wire off approximately one centimeter each and place a labeled tag on each. 

Crimping tool for wires

(Crimping tool for wires)

Reattach the wires

Reattaching the wires is inarguably a technical step and will require you to follow instructions keenly based on your manual. 

A man holding and reading the car user manual to check or fix the engine of a modern car

(A man holding and reading the car user manual to check or fix the engine of a modern car)

Briefly reconnect all the wires in order, then attach them back to their sources. Once done, securely press the wires, such as the battery cables, into their grommets and put things as they initially were. The process here involves a lot of crimping and will, therefore, take time. 

Test the wiring

It’s time to test if our wiring is correct. Here, you’ll first switch on the headlights. As you do so, ensure your dashboard has no illuminated warning lights. If there’s any warning light after starting your engine, turn off the system immediately and re-examine your wiring. 

Car dashboard warning lights

(Car dashboard warning lights)

After that, turn the headlights back and examine the electrical system. Watch for a faulty connection or wiring if there’s still an issue. 

Furthermore, you can replace the trim panels, for instance, the side skirts, located in the engine bay area’s opening access, and then close it.

Note: Rewiring a car is costly, depending on your car type, the type of damage, and the labor cost involved. But, often, it’ll range between $1200 and $1500. 

Alternatively, you can opt for secondhand Original Equipment Manufacturer

Original Equipment Manufacturer (OEM) wire harnesses cost less than their original counterparts. 

However, only a replacement will suffice if the wiring system has burnt or corroded sections. 


We hope you have learned something about rewiring your car as we conclude our article. 

The process isn’t as over-complicated as most people assume, provided you follow the instructions carefully and have the right equipment.

Otherwise, if you need further assistance, you can contact us

Hi I am Christa, sales manager of Cloom.

I have extensive expertise and experience in wiring harnesses and I believe I can help you.

And we have a very professional technical team who can clearly understand the customer’s needs and give professional suggestions and solutions after receiving the drawings.

If you also have wiring harness needs, please send me the drawing so that we can give you our quote and start our business.

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