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Hopkins Tow Doctor Vehicle End Test Unit

Hopkins Tow Doctor Vehicle End Test Unit

Item # HM50918
Our Price: $251.65
You Save: $151.45
Electrical Tools
Shipping Weight: 6 lbs
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  • Reviews (7)
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  • Videos (2)
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Hopkins Electrical Tools - HM50918

  • Testers
  • Tow Function Tester
  • Hopkins

  • Allows one person to check that a vehicle wiring harness has been installed properly and all functions are working
  • Tests all tow vehicle functions: ground, auxiliary power, brake, direction, and backup
  • Heavy-duty, 20' extension cord included
  • Adapts to 4-Flat, 6-Pole Round, or 7-way Blade

50918 Hopkins Tow Doctor Vehicle End Test Unit

50918 Hopkins Tow Doctor Vehicle End Test Unit

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Video of Hopkins Tow Doctor Vehicle End Test Unit

Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.

Video Transcript for Hopkins Tow Doctor Vehicle End Test Unit Review

Today we're going to be taking a look at the Hopkins Tow Doctor Vehicle End Test Unit, part number HM50918. Now you can check your vehicle's wiring harness without the need of a second person. The Hopkins Tow Doctor features a 20-foot heavy duty cable so you can check it from your cab. It tests ground, tail lights, left and right blinkers and brakes, back up, electric brakes and auxiliary power. It comes with adapters that will work with your 7-pole, 4-flat and 6-round in a convenient storage case to store it all. Now that we've gone over the features I'll go ahead and show you how it works. First thing we need to do is choose the appropriate adapter that we'll be testing.

I've got a 4-pole and a 7-pole. I'm going to be working with the 7-pole today. I'll grab my 7-pole adapter. Let's go ahead and plug that in. Make sure to push it all the way in then I'll plug the two ends together.

There we go. Now, I'll head up to the cab. As you can see I'm going to have more than enough cable to get there. Now I can run through all the functions without the need of anybody else. You can see I've already got power here with my auxiliary.

Now let's run through the running lights, which will just be the tail lights here. There we go. I know that works. Then the blinkers, left and right. Then both brakes.

It's even showing my electric brakes. Then we'll do the back up. Throw it in reverse. I know that works. Then I can even test my brake controller. We're all set. If I ever we're to lose ground, this would light up. That's going to complete our look at the Hopkins Tow Doctor Vehicle End Test Unit, part number HM50918.

Customer Satisfaction Score:

Customer Reviews

Hopkins Tow Doctor Vehicle End Test Unit - HM50918

Average Customer Rating:  5.0 out of 5 stars   (7 Customer Reviews)


Bought this item and also the trailer circuit tester. Both work great and save tons of time checking lights and brakes for the company fleet.


I have 4 trucks that tow trailers everyday, we have been trouble shooting the wiring for months. This tool has made solving all my electrical problems so easy!
Great tool


Works well to let you know if you've wired or are wired correctly. Big time saver. No more hours tracking down what the problem is. This device tells you when a circuit has no connection.


Worked as expected and has been very us eful.


Nice tool for testing trailer wiring.


So far so good. Just received the package today.


Good tool. Fast shipping.


See what our Experts say about this Hopkins Electrical Tools

  • Does Blinker Light of Hopkins Tow Doctor Tester # HM50918 Flash with Blinkers
    When you use the Hopkins Tow Doctor Vehicle End Test Unit # HM50918 to test the blinker functions the light on the display of the unit will blink with the blinker. If you check out the 1:20 mark of the video I attached you'll the red lights blinking when the blinkers are applied.
    view full answer...
  • Troubleshooting Electric Over Hydraulic Brakes that Do Not Apply
    If the brake controller appears to working properly and the brakes of your electric over hydraulic setup are still not applying that would lead me to believe that the problem is on the actuator itself. Does the actuator cycle on to build pressure when you connect it to your tow vehicle and the vehicle is turned on? If not, then the problem may be that the actuator is not getting the 12 volts it needs to power the unit. Typically, the 7-way of the trailer wiring powers the actuator through...
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  • Troubleshooting A Trailer Detection System That Is Working Intermittently On A 2021 Ford F-150
    Since your 2021 Ford F-150's trailer detection is working intermittently, that to me sounds like a grounding issue. What you can do is inspect your ground connections and ensure there is no damage to any of the wiring. Additionally, I also recommend unplugging your connections and applying some dielectric grease like the Dielectric Grease for Electrical Connectors, 2 oz. # 11755 and re-plug the connectors back in. If the issue still persists, you may need to take your truck to the dealer...
    view full answer...
  • Wiring Tester Kit for Both Vehicle Side and Trailer Side Connectors
    I do have options for you but we do not have an all inclusive tester kit that will test flat and round trailer connectors on both the trailer and vehicle. Instead you will want to use part # HM50928 for the trailer end and part # HM50918 for the vehicle end. Both kits have the ability to test 4-flat, 6-round, and 7-way connectors. I have attached a review video on both the vehicle side and trailer side tester kit for you as well.
    view full answer...
  • Does the Tow Doctor Trailer Side Tester Work on a Trailer with LED Lights
    The Tow Doctor for the trailer side is # HM50928. The other one, # HM50918, is the vehicle side. For the trailer side model it does not work if the trailer has LED lights. LED lights draw too little power for the tester to work properly. You could test the trailer side by using a separate 12 volt wire and applying power to each function. If the function does not work doing this test you know there is a wiring issue.
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  • 7-Way Tester that Tests Function of 7-way on Trailer
    We do have 7-way trailer wiring testers like with the Hopkins part # HM50918 which you'd plug your trailer 7-way into and it would put voltage on all of the pins to verify they are all working. This is a lot more involved than the opposite end tester which is why you'll notice it's a bit more expensive.
    view full answer...
  • Circuit Tester Needed for 7-Way on 2018 Chevy Colorado
    All of the circuit testers we carry, like the Tekonsha # 6562, are universal fits for vehicle connectors which is why these products aren't listed in our fitguide. The note on the product page about the Ford OEM brake controllers has more to do with the actual brake controller than the vehicle itself. If the notch on your 2018 Chevy Colorado is facing down then none of the other 7-Way testers like this will work and you either need to use a single prong tester like part # PTW2979 to test...
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  • Electric Trailer Brake Light Does Not Light Up When Testing with a Hopkins Tow Doctor Tester
    The replacement unit, # 4010509028 is a replacement for Tow Doctor part # HM50928. It looks like the Tow Doctor version you ordered is # HM50918. The difference is the HM50928 has more features. To test the brake controller output someone will need to sit in the truck and apply the manual override so that it is sending power back to the trailer connector. Otherwise, what will happen is what you are seeing, a slight flicker of light. That is the brake controller checking to see if a trailer...
    view full answer...
  • How to Bypass 12 Volt Trailer Wiring Accessory Circuit Not Functioning on New Ford Truck
    It would not as it's only really designed to see if voltage is present. The new Ford trucks need a specific amount of load on the circuits to activate the 12 volt circuit which is pretty annoying. If you are looking for a way to bypass that let me know as we can help.
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  • Comprehensive Vehicle Side Trailer Connector and Wiring Tester
    Most of the vehicle end trailer connectors we have will test for voltage on the circuits. If there was a short to ground then all of the lights would light up on the tester and you would know there is a problem. We do have a comprehensive trailer side tester, # 8010, which goes much further than any of the regular testers like # I26. But it is not designed for the vehicle side. For the vehicle side we have # HM50918 that can test multiple connector types on a vehicle (4-Flat, 6-Way round,...
    view full answer...
  • How to Extend the Reach of 7-Pole Round Adapter for Hopkins Tow Doctor Vehicle End Test Unit
    Thank you for your purchase of the Hopkins Tow Doctor Vehicle End Test Unit # HM50918, and I'm glad you are enjoying it! Hopkins doesn't make a version of the 7-Pole, Round-Pin Adapter # HM50944 with a longer wire lead, but you can still build out your own using 25' of this Deka Jacketed 7-Way Wire # DK74FR (sold by the foot) and then Vehicle End # PK11720 and Trailer End # PK11702 connectors. I reached out to my contact at Hopkins who confirmed this for me.
    view full answer...
  • Rubber Bumper for Stock Trailer
    We do have some rubber bumpers for you to install on your stock trailer. They are all 96" long so it just depends on what kind of width you're looking for: 96" Long x 2-1/16" Wide - # D2-96 96" Long x 3" Wide - # D3-96 96" Long x 4" Wide - # D4-96 These come pre-dilled with holes every 11" but you can cut these to length and drill new holes to match your application if you need to. Attached is a review video for you to check out.
    view full answer...

Do you have a question about this Electrical Tool?

Info for this part was:

Employee Michael H
Expert Research:
Michael H
Employee Jameson C
Expert Research:
Jameson C
Employee Jacob T
Video Edited:
Jacob T
Employee Dustin K
Video by:
Dustin K
Employee Cole B
Installed by:
Cole B
Employee Hayden R
Installed by:
Hayden R
Employee Wilson B
Updated by:
Wilson B
Employee Alexander C
Updated by:
Alexander C

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