Why Dash Lights Dim When Headlights Turn On

This phenomenon of dash lights going dim when the headlights are turned on is actually quite common and there are a few potential explanations. In this article, we’ll explore some of the reasons why dash lights dim when your headlights are turned on.

The potential causes can range from something simple like a bad dimmer switch or wiring issue to something more complex like a faulty alternator or battery. Regardless of the cause, we’ll discuss ways to diagnose and repair the problem. Knowing the cause will help you know the best solution and ensure your dash lights will remain illuminated at night.

So, if you’re experiencing this issue, keep reading to learn more about the possible causes and solutions. 

Why do my dash lights flicker when I turn on my headlight?

One of the most common questions people have when troubleshooting their vehicle is why their dash lights dim or flicker when their headlights are turned on. This phenomenon usually happens when the car is running low on voltage, meaning the electrical system is not supplying the necessary amount of power to the headlight system. This is usually due to a faulty alternator or a bad battery, both of which can be easily fixed. It can also be caused by a loose connection or a damaged wire, so it is important to check all the connections and wires leading to the headlight system.

Can a bad alternator cause the dimming of dash lights?

Yes, a bad alternator can cause the dimming of dash lights. When the alternator is malfunctioning, it cannot generate the required level of electricity to power the entire electrical system. This leads to the lights on the dash flickering or dimming when the headlights are turned on. This is due to the headlights drawing a large amount of power from the alternator, leaving the dash lights with little electricity to power them. 

dashboard light dimming

Reasons why your dashboard lights may be dimming

If your dash lights are dimming or flickering when you turn your headlights on, it’s important to determine the cause and take appropriate action. Taking the time to diagnose the issue now may save you from costly repairs and expensive headaches down the road. There are numerous reasons as to why your dashboard lights might dim when headlights are on but we will focus on these six:

1. Dim lights:

Many headlights often dim the dash lights automatically when they’re switched on, so this might be the cause of the problem.

If it’s not, look for the dimmer switch. This switch is responsible for adjusting the brightness of the dash lights. If you accidentally bumped it as a result of a bad road, you may have turned the light levels down without noticing it.

2. Instrument panel is dark:

Your car may have a blown fuse. Removing and replacing the old fuse should get the lights working again. While the new fuse may do the job, it can also indicate a deeper electrical problem. If the new fuse doesn’t stay long before going out, make sure that you have it inspected.

3. Electrical connections:

A faulty electrical connection may be causing the problem. This could be a loose connection in the headlight wiring or a problem with one of the components that send power to the dashboard. 

4. Flickering lights:

If your instrument panel is flickering, it’s likely not going to be a problem with the dash lights at all. The car battery could be faulty, or the alternator could be going bad. You should diagnose this problem and replace whichever part is faulty. 

5. Headlight wiring:

A problem with your headlight wiring may be the culprit. If this is the case, the wiring could be shorting out, causing the dash lights to flicker or dim.

Possible ways to fix dim dash lights

Dash lights dim or flicker when headlights are activated due to a variety of possible causes. To fix this issue, you’ll need to identify the cause and then follow one of the four possible repair solutions. 

  • Check the headlight switch to make sure it is functioning properly.
  • Test your alternator and voltage regulator to make sure they are in good working order.
  • Inspect the ground connection to ensure it is tightly secured.
  • Then, try replacing the headlight switch with a new one if none of the other solutions has worked.

Step-by-step ways to take precautions against dimming dash lights

Dash lights dim and flicker when headlights are on because of an insufficient electrical connection. Taking the necessary precautions to prevent this from happening is essential to ensure your car’s safety and performance. Here are five step-by-step ways to take precautions against dimming dash lights: 

  • Check the fuse box. Make sure all the connections are properly done and that the fuses are in place. 
  • Check the wiring for any faulty connections and make sure to replace them if necessary. 
  • Check the alternator for any signs of wear and tear and replace it if necessary. 
  • Clean the headlight terminals and all the wiring connections they have. 
  • Use corrosion-resistant materials to protect the wiring and terminals from any further damage. 


Regular maintenance and troubleshooting of your car’s electrical system is the best way to identify and address the issue before the battery dies or another damage occurs.


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