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How Do You Test the Ground on a Trailer Plug With a Multimeter?

Home » Blog » How Do You Test the Ground on a Trailer Plug With a Multimeter?

Feb 13, 2024 | News

Grounding on a trailer enhances electrical safety, prevents shocks, and stabilizes voltage, promoting efficient and reliable operation. At David’s Heavy Duty Tool Sales, we can help you find suitable trailer tester equipment to check for continuity in a trailer plug. A multimeter measures various electrical properties, including voltage, current, resistance, and continuity. Here are ways to test the ground on a trailer plug with a multimeter:

Set Up Your Multimeter

To power your multimeter:

  1. Use the power or function knob located on the front or side of the device.
  2. Choose the appropriate mode for the test.
  3. For testing continuity or resistance, select the correct mode on the multimeter. When using the continuity mode, look for a sound symbol on the multimeter.

This symbol indicates that the multimeter emits a sound when the device detects continuity.

The multimeter may also indicate the continuity mode. In this mode, the multimeter produces a beep when it senses a complete circuit. If the multimeter has a range adjustment feature, set the range to an appropriate value for the expected resistance or continuity level. Our multimeters have automatic ranging, making it easy for users to set resistance values.

Identify the Ground Pin 

When identifying the ground pin on a trailer plug, look for symbols such as G, GND, and Ground. The ground pin may be color-coded differently than the other pins. Color coding can vary, but the ground pin is often white or black. If you need help identifying the ground pin through visual inspection or documentation, contact us at David’s Heavy Duty Tool Sales for clarification. Our team can provide specific information about pin designations.

You can also use a multimeter to identify the ground pin by setting it to a continuity mode. In this mode, touch one probe to a known ground and use the other probe to test each pin on the trailer plug until continuity is detected, signifying the ground pin. Overload protection in our multimeters helps protect the tool from potential damage from voltage spikes.

Locate The Ground Point and Probe It

To locate the ground point on the trailer, trace the white ground wire from the trailer plug along the trailer’s wiring harness. The wire should lead to the point where it is securely attached to the trailer frame or another grounding surface. Inspect lights, brakes, or other electrical components on the trailer. Manufacturers establish ground connections at or near electrical components.

After identifying the ground point, insert the multimeter’s red probe into the correct spot. Hold the red probe firmly against the ground point to maintain a stable and secure connection during the test. 

Check For Continuity

Check if this trailer tester equipment is set to continuity or resistance mode to check for continuity. Keep the negative probe connected to the ground pin on the trailer plug and the positive probe on the known ground point on the towing vehicle. Touch the multimeter probes simultaneously to the ground pin and the known ground on the towing vehicle. If in continuity mode, you can hear a beep, indicating a complete electrical circuit. A positive result in continuity mode signifies a proper ground connection. With the backlit display on our multimeters, you can read the results when testing the ground at night or in dimly lit areas.

Observe the multimeter display for a low resistance reading close to zero ohms when using the resistance mode. The reading helps to determine if there’s a good electrical connection between the ground pin on the trailer plug and the known ground on the towing vehicle. If testing multiple ground points on different components, repeat the process by selecting another known ground point and checking for continuity.


If there is no continuity or the resistance is too high, there may be an issue with the ground connection. Inspect the ground wire for visible damage, such as cuts, abrasions, or fraying. If you find any damage, replace the ground wire to boost normal functioning. You can also inspect the connections at both ends of the ground wire on the trailer plug and the vehicle’s ground point.

Use a wire brush or sandpaper to remove dust or dirt on the metal surface. You can also check for bent or pushed-in connector pins and straighten them. After making corrections, probe the new ground point with the multimeter and check for continuity or low resistance. Our multimeters offer real-time monitoring capabilities, allowing you to observe changes in continuity or resistance as you adjust the plug’s wiring.

Invest in Quality Trailer Tester Equipment

Multimeters check for continuity mode and resistance to indicate good or poor ground connection. These tools have safety features, resistance, and continuity modes to help you test the ground on a trailer plug. Browse our collection of diagnostic tools to invest in trailer tester equipment.