Testing 7-Pin Trailer Plug With A Voltmeter/Multimeter | How to Test

Everybody needs to be a little bit of a handyman sometimes. Whether it is in your home changing the bulb or fixing a plug socket, or fixing the car turn lights, it is the same thing. You need to have some electrical idea before you proceed with taking apart any of these. Yes, you have to test them beforehand so you can know what is the fault. 

For your car, truck, camper, or RV, you get a 7-pin trailer plug for all the light wiring. And if any of them are faulty, you can simply open the 7-pin plug and test them. But what is the process of testing 7 pin trailer plug?

Well, you will need a volt meter or electric meter with black and red probes for one. Then proceed on taking apart the plug and start testing them one by one. We should also mention, you have to keep your vehicle running during this time. 

So let’s get you through the process to make it a bit easier, shall we?

Testing 7-Pin Trailer Plug With A Voltmeter Multimeter

3 Easy Steps For Testing 7-Pin Trailer Plug With A Voltmeter/Multimeter

To test the trailer plug, you can always use a standard electric tester, which will light up. More modern ones will also show you a voltage flow. But that’s not a good enough solution. You have to get a clear reading. And this is where the voltmeter comes in. Oh! Also, make sure to wear a pair of work gloves, so you don’t get an electric shock from your own battery.

Here is a chart of all 7 pins to give you a clear understanding of which pin is for which light and function. 

Pin NumberFunction (s) Of The Pin
Pin 1Left indicator/Brake light
Pin 2Backing light/Reverse light
Pin 3Ground 
Pin 4Right turn light/ Brake light
Pin 5Electric brake light
Pin 6Battery supply
Pin 7Auxiliary or charging wire

Here are steps to test 7-Pin Trailer Plug –

Step 1: Unplug The 7 Pin And Turn On The Voltmeter

Put on your working gloves and unplug the 7-pin plug. Proceed on turning on the voltmeter/multimeter. When the numbers turn out zero, it is your queue to start. 

Step 2: Connect The Black Probe To The Ground Pin Of The Plug

Insert the black probe of your voltmeter into the ground pin (Pin 3). You can also place it on your car’s metal body, which will do the same thing. And proceed on testing the first pin. Pin 1 is most of the time the left in turn and brake lights. So make sure to turn on the indicator and tell someone to push on the brake lever. Test them separately. If the voltmeter says 12V or 48V, or your batteries volt, then the flow is fine. The wiring is A-okay and you can proceed to test the next pin.

Step 3: Touch Each Pin To Check The Reading

Do the same thing with all the pins. Keep the black probe in the ground pin and check with the red probe on each pin. If any of them show something different than your battery’s volt, you have a problem with that wiring. Make sure to turn on the specific button, or lever while you are testing the designated pin. 

Note: Sometimes the ground pin placement is different. This is due to different manufacturers. So make sure you check which one is your ground and proceed from there.

Frequently Asked Questions and Answers (FAQs)

What voltage should a 7-pin trailer light be?

The normal voltage of a 7-pin trailer light should be 12V as it is designed for that. But some do exist for a 6V and a 24V battery. But they are very rare to find. 

Are trailer lights 12V or 24V?

The most common trailer lights today are 12V. Older vehicles used 6V lights and some bigger trailers use 24V systems. 

How do I check if a plug is properly grounded?

To check if a plug is properly grounded, the easiest way is to turn on your multimeter on the max settings. Insert the two probes into the live connection and ground one. Record the reading. Now if you take out the black probe and insert it into the third pin, you will see that it will show you the same reading, not different. 


Remember to practice safety at all times. As working with a car battery might not seem as dangerous as working with a house electrical outlet, it is the same thing. If you don’t have any idea what you are doing and feel uncomfortable, make sure to ask for professional help. 

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