How to Test Voltage Switch on MIG Welder: A Comprehensive Guide

When it comes to maintaining and troubleshooting a MIG welder, one of the critical components to check is the voltage switch. This switch plays a crucial role in regulating the output voltage of the welder, ensuring that the correct voltage is applied to the welding process. Improper functioning of the voltage switch can lead to various issues, such as inconsistent weld quality, excessive spatter, or even damage to the welder itself. In this comprehensive guide, we will delve into the step-by-step process of testing the voltage switch on a MIG welder, providing you with the technical expertise and hands-on knowledge to diagnose and address any voltage-related problems.

Preparing for Voltage Switch Testing

Before you begin testing the voltage switch, it’s essential to ensure that you have the necessary tools and equipment. You will need the following:

  1. Multimeter: A digital multimeter is a must-have tool for testing the voltage switch. It will allow you to measure the resistance and voltage at different points in the circuit.
  2. Cleaning Supplies: A contact cleaner or a small amount of isopropyl alcohol can be used to clean the voltage switch contacts, if necessary.
  3. Personal Protective Equipment (PPE): Wear appropriate PPE, such as welding gloves, safety glasses, and a welding jacket, to protect yourself during the testing process.

Checking the Voltage Settings

how to test voltage switch on mig welderImage source: Mig weld example

The first step in testing the voltage switch is to ensure that the voltage setting is correct. Locate the voltage switch on your MIG welder and check that it is set to the appropriate voltage for the welding task at hand. Consult your welder’s manual or manufacturer’s recommendations to determine the correct voltage setting.

If the voltage switch is set to a higher voltage than necessary, it can cause various issues, such as excessive spatter, poor weld penetration, and even damage to the welder’s components. Ensure that the voltage switch is set to the recommended setting before proceeding with further testing.

Verifying the Power Supply

Next, you’ll need to check the power supply to the welder. Use your multimeter to measure the voltage at the wall outlet or power source that the welder is connected to. Ensure that the voltage matches the welder’s input voltage requirements, as specified in the manufacturer’s documentation.

If the power supply voltage is not within the acceptable range, it could be the root cause of the voltage switch-related issues. In such a case, you may need to address the power supply problem before testing the voltage switch further.

Inspecting the Wiring

Carefully inspect the wiring connections between the voltage switch and the power supply. Look for any loose, damaged, or corroded wires that could be causing intermittent or incorrect voltage readings.

Use your multimeter to check the continuity of the wires, ensuring that there are no breaks or high-resistance points in the circuit. If you find any issues with the wiring, address them by tightening connections, replacing damaged wires, or seeking the assistance of a qualified electrician, if necessary.

Testing the Voltage Switch

To test the voltage switch, you’ll need to use your multimeter to measure the resistance between the different switch positions. Follow these steps:

  1. Disconnect the welder from the power source: Ensure that the welder is unplugged or the circuit breaker is turned off to prevent any risk of electric shock.
  2. Locate the voltage switch: Identify the voltage switch on your MIG welder, usually located on the control panel or the back of the machine.
  3. Set the multimeter to measure resistance: Configure your multimeter to measure resistance (Ω) or continuity.
  4. Test the switch positions: Place the multimeter probes on the terminals or contacts of the voltage switch. Slowly move the switch between the different positions and observe the resistance readings. The resistance should change as you move the switch, indicating that the switch is functioning correctly.
  5. Check for continuity: In each switch position, check for continuity (a reading of 0 Ω or close to it) between the appropriate terminals. This ensures that the switch is making a proper connection in each position.
  6. Document the readings: Record the resistance and continuity readings for each switch position. This information can be helpful for future reference or if you need to replace the voltage switch.

If the resistance readings do not change as you move the switch, or if you don’t detect continuity in one or more positions, the voltage switch may be faulty and in need of replacement.

Checking the Welder Output

Finally, you can use your multimeter to check the output voltage and amperage of the welder. This will help you determine if the voltage switch is affecting the welder’s performance.

  1. Set the welder to the desired voltage setting: Adjust the voltage switch to the desired setting.
  2. Measure the output voltage: Connect the multimeter probes to the welder’s output terminals or the welding cable connections. Observe the voltage reading and compare it to the expected output voltage for the selected setting.
  3. Measure the output amperage: If your multimeter has the capability, you can also measure the output amperage of the welder. This can provide additional insights into the welder’s performance and the impact of the voltage switch.

If the output voltage or amperage readings are significantly different from the expected values, it may indicate a problem with the voltage switch or other components in the welder’s electrical system.

Repairing or Replacing the Voltage Switch

If the voltage switch is found to be faulty, you have a few options for addressing the issue:

  1. Clean the switch contacts: Use a contact cleaner or a small amount of isopropyl alcohol to clean the switch contacts. This can sometimes resolve issues caused by oxidation or buildup on the contacts.
  2. Replace the voltage switch: If cleaning the contacts does not resolve the problem, you may need to replace the voltage switch entirely. Consult your welder’s manual or manufacturer for the correct replacement part and follow their instructions for the replacement process.

It’s important to note that if you are not comfortable performing these repairs yourself, it is recommended to seek the assistance of a qualified welder technician or service center. Improper handling of electrical components can be dangerous and may lead to further damage to the welder.


Maintaining and troubleshooting the voltage switch on a MIG welder is a crucial aspect of ensuring the proper operation and longevity of your welding equipment. By following the step-by-step process outlined in this comprehensive guide, you can effectively test the voltage switch, identify any issues, and take the necessary steps to address them. Remember to always prioritize safety and consult the manufacturer’s instructions or seek professional assistance if you are unsure about any part of the testing or repair process.


  1. Voltage switch | MIG Welding Forum
  2. Fix a Mig welder your guide to troubleshooting a MIG welder (any brand) not working or broken – YouTube
  3. how to check voltage output on a mig? – WeldingWeb