Availability of 7-Way Tester for Trailer Wiring

Updated 11/13/2025 | Published 11/10/2025

Question:

A 7 flat pin trailer plug tester from the trailer. I have a tester that checks the tow vehicle receptacle. Is there anything out there?

asked by: Wayles H

Expert Reply:

Hey Wayles, we do have the type of tester you are looking for with the Hopkins # HM50928. I know it's probably more expensive than you anticipated but to test the functions on the trailer it requires current be applied to each circuit that is normally created by the tow vehicle so it's a bit more involved than testing the vehicle 7-way. Is your trailer wiring giving you problems?

expert reply by: Jameson C

Wayles H.

11/11/2025

Thanks for your speedy reply. There was a problem with the trailer 7 way plug. I changed the plug on the trailer cord and the tow vehicle's receptacle. I would in turn start the tow vehicle, turn on the headlights and 4 way flashers. I would then walk around the trailer to check the lights. All seemed OK. Now with everything OK, I would drive my vehicle then turn on the trailer haul button. After a few yards or miles the tow vehicle's info screen would beep, saying "Check your trailer connection". The trailer lights would still be working. I then turned off the trailer haul button and the beeping stopped. No more warning signs. I later took the trailer plug apart and attached ring terminals on the 6 wires and put the plug back together. That is why I want to check the trailer wiring. I even looked for the wiring diagram to make sure everything was in the right spot. Later, I checked the vehicle's sensor block under the dashboard to check for any problems. It came back saying my hood was open and a window was down. I checked the fuses, all OK. I am just stumped on this problem. I do not want to go to my dealer and pay $$$ to get it fixed.

Jameson C.

11/11/2025

@WaylesH Does the trailer have LED lights by chance? They have a tendency to cause dash error messages since they don't have as much of an amperage draw as incandescent bulbs. Otherwise typically this problem is caused by a bad ground on the trailer wiring...but you changed the connectors so that should have addressed that. Does the trailer have brakes? If so, are they working currently?

Wayles H.

11/12/2025

@JamesonC Yes this trailer (camper) has LED lights, they all work fine. There was a problem with the brakes, it turned out that I had the left and right turn signal in the wrong place. I switched the to the correct terminal, all was good. The ground wire (yellow) in the center of the plug, I made it a little bit longer. I remember while putting both plug and receptacle together, there was a small bag of grease. I put it on the terminals. My son suggested a can of contact cleaner spray. Have not tried it. No moister has gotten in on either units.

Jameson C.

11/12/2025

@WaylesH So everything was working fine on the dash prior to the issue you had but now it's showing that message? The center pin of a 7-way isn't typically a ground circuit.