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RV Lights Dim When Furnace Comes On

When you’re out on the road in your recreational vehicle (RV), it’s essential to have all your systems working properly to ensure a comfortable journey.

One common issue that RV owners may face is the dimming of lights when the furnace comes on.

This can be a frustrating problem, especially when you rely on your lights for visibility and safety while traveling.

In this article, we will delve into the reasons behind this phenomenon, explore possible solutions, and provide helpful tips to prevent and troubleshoot the issue.

So, let’s shed some light on the topic of “RV lights dim when furnace comes on” and find the best way to tackle it!

RV Lights Dimming: Why Does It Happen?

The dimming of lights in an RV when the furnace is activated is primarily due to a power supply issue.

The furnace requires a significant amount of power to function, and when it starts, it draws power from the same source as the lights.

This sudden increase in power demand can cause a drop in voltage, leading to a dimming effect.

Understanding the underlying causes will help you address the problem more effectively.

Let’s take a closer look at some common reasons for this issue:

Insufficient Battery Capacity

One possible cause of dimming lights is an RV battery with insufficient capacity.

RVs rely on batteries to power their electrical systems, including lights.

If your battery is not adequately sized or is nearing the end of its life, it may struggle to supply the necessary power when the furnace kicks in.

This can result in a voltage drop, causing your lights to dim.

Loose or Corroded Electrical Connections

Another culprit behind dimming lights could be loose or corroded electrical connections.

Over time, vibrations from the road and natural wear and tear can loosen connections or lead to corrosion.

When the furnace activates, it places additional strain on the electrical system, exacerbating any existing connection issues.

These poor connections impede the smooth flow of electricity, causing voltage drops and subsequent dimming of lights.

Undersized Wiring

In some cases, the wiring in an RV may not be adequately sized to handle the power demands of both the furnace and the lights simultaneously.

When the furnace starts, it draws a substantial amount of current, and if the wiring is too small, it can hinder the flow of electricity.

As a result, the lights may dim as they receive a reduced voltage.

Weak Alternator or Converter

The alternator or converter in your RV plays a crucial role in charging the batteries and supplying power to the electrical system.

If the alternator or converter is weak or malfunctioning, it may struggle to provide sufficient power to both the lights and the furnace.

This inadequate power supply can lead to dimming lights when the furnace comes on.

Troubleshooting and Solutions

Now that we understand the potential causes of the issue, let’s explore some troubleshooting steps and solutions to resolve the problem of dimming lights in your RV when the furnace is activated:

Check Battery Capacity

Begin by checking the capacity of your RV’s battery.

If it is undersized or nearing the end of its life, consider upgrading to a higher-capacity battery.

A battery with greater reserve capacity will provide a more stable power supply and minimize voltage drops when the furnace starts.

Inspect Electrical Connections

Thoroughly inspect all electrical connections in your RV. Look for loose or corroded terminals, wires, and connectors.

Tighten any loose connections and clean off any corrosion using an appropriate electrical contact cleaner.

Ensuring secure and clean connections will improve the flow of electricity and reduce voltage drops.

Upgrade Wiring

If you suspect that undersized wiring is causing the issue, consider upgrading the wiring in your RV.

Consult an RV technician or electrician to determine the correct wire gauge for your specific electrical system.

Upgrading to appropriately sized wiring will allow for smoother power transmission and help prevent lights from dimming when the furnace operates.

Test the Alternator or Converter

To check the health of your alternator or converter, use a multimeter to measure the voltage output.

If the reading is significantly lower than the recommended range, it may indicate a problem with the unit.

In such cases, consult a professional to repair or replace the alternator or converter, ensuring a reliable power supply for your RV.

Consider an Auxiliary Power Source

If the above solutions do not resolve the issue, you can explore the option of adding an auxiliary power source dedicated to the furnace.

Installing a separate battery or generator specifically for the furnace will alleviate the strain on the main electrical system, ensuring that the lights remain unaffected when the furnace comes on.

Frequently Asked Questions (FAQs)

Why do my RV lights dim only when the furnace starts?

When the furnace starts, it draws a significant amount of power, causing a temporary voltage drop. This drop leads to a dimming effect in the lights.

Can I replace my RV battery with a higher-capacity one to solve the issue?

Yes, upgrading to a higher-capacity battery can help stabilize the power supply and minimize voltage drops. However, it is essential to ensure compatibility with your RV’s electrical system.

Is it necessary to consult a professional for upgrading the wiring in my RV?

While it is possible to upgrade the wiring yourself if you have the necessary knowledge and experience, it is recommended to consult an RV technician or electrician to ensure proper installation and compliance with safety standards.

How can I determine the correct wire gauge for upgrading my RV’s wiring?

Consulting an RV technician or electrician is the best way to determine the appropriate wire gauge for your RV’s electrical system. They will consider factors such as power requirements and wire length to provide accurate guidance.

Are there any safety precautions I should take when inspecting electrical connections?

Always ensure that the power supply is disconnected before inspecting or working on electrical connections in your RV. This precaution will prevent accidental shocks or short circuits.

What should I do if none of the troubleshooting steps resolve the issue?

If you have exhausted all troubleshooting steps and the problem persists, it is advisable to seek professional assistance from an RV technician. They will have the expertise to diagnose and resolve the issue effectively.


Dimming lights in an RV when the furnace comes on can be a result of various factors such as insufficient battery capacity, loose connections, undersized wiring, or a weak alternator or converter.

By following the troubleshooting steps outlined in this article and implementing the suggested solutions, you can alleviate the issue and enjoy uninterrupted lighting in your RV.

Remember to check the battery capacity, inspect electrical connections, upgrade wiring if necessary, test the alternator or converter, and consider adding an auxiliary power source if needed.

By taking proactive measures, you can ensure a comfortable and well-lit journey in your RV.