Five-Star Manufacturer
Fast Delivery
Customized Service
HomeTips & Guides65 Mustang Wiring Harness – How to Install Each

65 Mustang Wiring Harness – How to Install Each

If you seek to restore your 1965 Mustang one of the things you need to do is install modern wiring. After all, modern wiring harness features better insulation for current consistency and connectors and wiring for modern accessories upgrades. For this reason, I bring you steps to install each 65 Mustang wiring harness to help upgrade your car.


Collecting materials and tools

Before connecting any harness, get a detailed and color-coded wiring diagram of your Mustang. Doing so makes your wiring easier and reduces confusion during the process.

Some tools you may want include a grinder, pliers, electrical tape, flathead screwdriver, hole saw, wire stripper, drill, and flashlight.

Once you have all the materials, you need to separate each of your new harnesses and then remove the old one. Doing so helps you become organized and plan where to start the process.

Removing the old harness

To do this, you must first read your manual thoroughly to understand the expectations of each wiring harness. Then, unbox and unwrap your new wiring harness and study where the connectors are.

However, ensure not to unwrap the connectors, terminals, and pigtails to avoid losing them. Then disconnect and remove your battery to avoid accidents and give you ample space during installation. 

Now remove your old wiring harness, starting from the headlights and moving to the back. Once you get to any ground wire, cut it from the harness but leave it terminals.

You may now remove your ignition wiring nut that secures your Mustang wiring behind your gauge cluster. Last, use a flathead screwdriver to free the tabs that hold your trunk harness in place for easy harness removal.

Installation tools you may need

Installation tools you may need

Gauge Cluster Harness

Hoping you have your tools and the correct wires for your model, it’s time to wire your cluster gauge harness. 

  • Start by putting your fuel gauge harness ring terminals in their place on the gauge bolt. While here, ensure you secure them snuggling using their nuts to avoid coming off.
  • From there, put your panel bulbs in their respective sockets. You may now thumb your panel lamp connection in holes with blue inserts on the cluster. Now, identify the oil bulb assembly from your cluster and insert it tightly into its hole on the fuel gauge side. Remember to do the same for the alternator bulb you install in the hole on the temperature gauge side.
  • Once through, now take the other two remaining panel lamp assemblies and install them on the remaining cluster’s holes.
  • Now, take your turn signal indicator harness, connect a bulb to its socket, and put it in the hole under the alternator. Then, do the same for your high beam indicator harness and connect it to the hole under your oil gauge.
  • Then, identify your constant voltage regulator, take its female and male connectors, and insert them into their plugs.
  • Lastly, connect the signal light wire ring terminals on the bolts and use nuts to hold them tightly in place.
Colored wires for a car

Colored wires for a car

Underhood Harness

Your Mustang underhood harness connects headlights, regulators, washer nose, horn, and others. I recommend following the steps below to wire it correctly:


First, check your old harness and remove the attached capacitor, making sure not to destroy it.

Then, you must strip about an inch of the regulator yellow wire from your underhood harness. From there, install the supplied female connector on it and then connect the male connector of the capacitor to it.

While holding the new harness, locate the black ground wire from its regulator. You may use your cable stripper to strip its insulation and install a ring terminal. 

Install grounding and position the harness in place.

Now identify the two ground wires (grey) for your headlight plugs on the harness. Stip their insulator at the end and then install a female butt connector on each.

Now, wrap your harness around your Mustang engine bay, beginning from the wire cluster on the driver’s side. The harness must run to the driver’s side headlight connection and the regulator.

From there, it goes to the horn, passager headlight connector, and the alternator.

Connect voltage connector and regulator.

Once done, pass the driver’s side parking and headlight harness through the engine bay hole found on its front. Now, connect your voltage connector to its plug on your underhood harness.

Then, place the regulator in its position and attach the ground wire you made to its top bolt. While here, also connect the mounting of the radio suppressor to the bottom bolt of your regulator.

From there, install a female spade connector on your washer hose wire end and plug it into the existing washer hose connection. Take your two yellow horn wires and pass them through the engine compartment, then connect them to their respective horns.

Ground the headlight and taillight wiring.

In this step, ground your headlights and use a wrench to secure them tightly. Note you ground the driver headlight on the regulator top bolt while the passenger headlight into the factory grounding area.

Now, pass the passenger parking light and headlight harness through the hole in the front of the engine compartment. Now, you have only one grey wire across the engine compartmen for an electric fan.

If you don’t have immediate needs for the fan, ensure you tie this wire to get it out of the way.

Connect the parking and headlight harness.

From there, find the harness for the parking and headlight for both the driver and passenger side. Then, feed them through the small hole in the headlight housing and connect their connectors.

Once done, you may now connect the whole harness to your alternator. Now, use a hole saw to widen the firewall holes for the new harness, plates, grommets, and connectors.

Then, feed the harnesses and their connectors through the plates and grommets and secure them using the provided hardware. Lastly, install a fuse box behind the gauge cluster and secure it with the provided screws.

Connect headlight wires

Connect headlight wires

Main Harness

Now, the main harness installation is the most demanding but with the steps below, you can get it right.

Put your main harness in place.

Position your main harness below your car dashboard and pass it through the cluster gauge hole. Now, pull until everything is almost in its position. While here, remove your wiper switch to make the installation possible.

You can do this by unscrewing it’s tightening hardware on the knob, then remove the knob first. From there, uninstall its ring under the knob and remove the wiper switch from the dashboard.

Connect wiper harness

Now identify your wiper wiring and connect all its connectors (5), which you can find in the switch’s back. When done, return the wiper switch to its position on the dashboard and secure it as it was.

From there, check your manual to identify the grounding of your main harness and its installation holes. Clean the grounding of paint and corrosion and then connect the ground wire to the bolts.

Next, pass your wiper wiring through the dashboard and link it to its factory connectors.

Connect your ignition switch wiring.

Here, you will pull the rest of the main wiring via the dashboard hole to prepare for other installations.

Now identify your ignition wiring terminal (grey) and connect its ring to its position on the ignition plug stud. You may now attach the ignition plug to its existing factory switch.

Now, place the turn signal cable and switch on your brake release handle. Connect the harness’ white connectors to the turn signal switch at the bottom.

Remember the switch box you installed on the underhood harness section? Well, it’s time to connect the main harness to its position on that switch box. 

Other components connection

Hoping you placed each connection almost in its position, it’s time to plug in other components. You can start with brake light switches, cigarette lighter wires, high beam switches, a radio, and heater motors. Ensure you follow the manual and the wiring diagram to make each installation correct.

Mai harness connection

Mai harness connection

Rear Harness

After the main harness wiring, it’s the rear harness wiring which is simple using the steps below.

  • First, feed the main harness into the trunk through a hole on the driver’s side and put it in place ready to install. You may now secure the wiring under the carpet or the driver door sill.
  • From there, identify the drive side taillight pigtails and connect them to the green and black main harness wires. You may do this by first installing butt connectors, then plugging in, then doing the same to the passager side.
  • Next, connect the driver and passenger side backup lights to their respective pigtails on your main harness.
  • Finally, connect the license plate wire to its position on the main harness, and that’s it.

Rear wiring sockets

Engine bay Connection

  • You first need to install a ring terminal on the two grey battery mounts. Then, install a fuse in the engine bay and connect both wires to the fuse bolts.
  • Now connect the black battery wire to the solenoid’s side and secure its ring terminal.
  • Identify your red battery cable and connect it to the solenoid’s front terminal.
  • Finally, connect the brown wire to the remaining terminal on the solenoid next to the red wire.

Organize Wires and reconnect the battery.

Hoping you have successfully installed these harnesses. Now, it’s time to organize wires properly to ensure neatness. Here, you can bundle likes wires together and use cable ties to secure them.

Then secure any naked joint using an electrical tape and check if all connections are snug. From there, you can clean up, reconnect your battery, and take a test ride.


With my detailed steps, you can upgrade your 65 Mustang wiring harness. However, remember that you need patience and time to do a successful job.

I am Lillian Yang, having been a sales manager for over 10 years.

I have received many positive reviews from customers. They have praised our excellent service, on-time delivery, and high-quality cable assemblies.

For your projects, please provide cable assembly files/images/smples, etc., so that I can send you a quotation within 24 hours.

Contact me now and let’s get started on building your wire harnesses!

Background media

For Better Future
and Business
Let’s Talk Now!

Fill in your details and we’ll get back to you in 24 Hours.

Contact Form Demo


[email protected]




3rd Floor, Nanhai Plaza, NO.505 Xinhua Road Xinhua District,
Shijiazhuang, Hebei, China. 050057


© 2007- 2023 Cloom tech. ALL RIGHTS RESERVED.



Subscribe to our newsletter for the latest updates, exclusive offers, and exciting news delivered straight to your inbox.