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HomeTips & GuidesHeadlight Connector Plug – Types, Installation, and Diagnosing Tips

Headlight Connector Plug – Types, Installation, and Diagnosing Tips

About Headlight Connector Plug: Car headlights are electrical components that most car owners are often unfamiliar with until they become faulty. As a last resort, they can choose to replace the corroded/damaged connector or fix it. And that’s where we come in. 

Safely fixing a broken connector is easy but a little tricky. However, following the instructions in our article to the letter, you’d have made the road safer for all users. In addition to the instructions, we’ll teach you how to diagnose a spoilt headlight socket and the connector types. 

What’s a headlight connector?

A headlight connector is an electric component that acts as a link between the power supply of the vehicle and its headlight bulb. Subsequently, the bulb illuminates the road thus making it safe for drivers and pedestrians.

Car headlight with connector

(Car headlight with connector)

As such, when it malfunctions, it can hinder road safety. 

Types of headlight connectors

Headlight connectors are different depending on the vehicle you’re using. If you figure out your car’s ideal connector, you’ll be good to go. 

The most common examples are in the table below.

Components Types 
Reverse lights W21W, T20, 7440
Turn signals P21W (mainly for primary turn signals)
Side direction signals W53, T10, T4W
Fog lightsH8, H10, H11
Headlamps H7, H15, HB3, H9, H4
An H4 type of halogen bulb and a replacement socket

(An H4 type of halogen bulb and a replacement socket)

How do you diagnose a melted headlight connector?

Generally, bulb sockets in older and newer cars work similarly. The sockets connect the electrical system to the headlight bulbs and ensure their functionality.

However, due to external weather conditions, the socket may sometimes experience corrosion or wear out. Consequently, the bulb won’t work because of the disrupted voltage transmission. 

Therefore, it is crucial to initially diagnose the malfunctioning bulb socket before replacing or fixing it. 

Equipment needed

Test lights and jumper cables

Red and black jumper cables for car battery

(Red and black jumper cables for car battery) 


  1. Find the headlight bulb socket 

First, locate the socket below the car or via the engine compartment. Both ways will let you in at the rear side of the headlight assembly. 

  1. Operating the accessory mode

Secondly, turn your key into an accessory mode. The process allows power to get to the vehicle accessories like headlights despite the engine being off. 

You can turn the signal on and let it flash before diagnosing if there’s a faulty turn signal bulb socket. 

  1. Connecting the test light 

A test light is necessary for testing the ground and power of the defective bulb socket. Now that your hood is open use a jumper cable to link the test light with the battery’s positive terminal. 

Next, find a good ground. Ideally, it can be a clean metal and unpainted surface below the vehicle’s hood. To confirm the light works, touch the surface using the test light’s tip.

  1. Testing the headlight bulb socket 

Repeat the testing procedure in the third step here but on the bulb sockets. As such, you’ll use the test light on the meta contacts to ensure the ground is working.

A man holding a car headlight plug to check for irregularities during car maintenance

 (A man holding a car headlight plug to check for irregularities during car maintenance) 

Furthermore, you may scratch off some corrosion to get a steady light when using the test light. However, an unsteady light and corrosion indicate a severely damaged headlight socket that requires replacement. 

How to replace a bad headlight socket

0.A man inserting car headlights to replace a broken bulb

(A mechanic changing a car headlight in a workshop)

Now that we have diagnosed the problem and confirmed its location let us fix it. For this procedure, you’ll need some tools. They include a tape and socket wrench. 

With the tools at hand, use the guidelines below. 

  • First, use your socket wrench to remove the wire at the battery’s negative terminal and place it in a different location.
  • Next, disconnect the bulb from the socket and set it aside. Also, remove the bulb socket from the headlight connector and clean it.
  • Attach a new headlight connector and bulb and secure it with tape.

Note: Ensure you know your car’s type of light bulb before replacing it since it’ll also dictate the type of bulb socket to use. 

  • Finally, use a test light to verify that it’s working properly. 


We have highlighted all you need to know, from the types of headlight connectors to diagnosing and eventually fixing a broken one. 

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.

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