Are round plug trailer harnesses grounded thru hitch?

[Fordiesel69]

We own a gatormade car hauler trailer that sits outside. It has the round trailer connector with the electric trailer brakes. The hitch sits in our garage which is not climate controlled.

Ever time we go to use it, the lights are not stable and we get trailed connected / trailer disconnected messages on our trucks every time we use it, until the rust wears off the ball and hitch.

So on sat I wire brushed and sanded the hitch and the ball, and curled up a piece of sandpaper in the ball socket. No more issues now.

Does this mean the trailer requires a ground elsewhere?

 

[GON]

The seven pin has a ground, but if that ground is "open", then the hitch system may provide a ground. Your trailer lights should work even if the trailer is not hooked up to the tow vehicle via the hitch.

 

[John105]

My assumption whenever I saw them was that such vehicles have a trailer brake controller. I don't believe that's a true statement.

Example: the Chevy Tahoe RST Performance Edition. It has the brake controller deleted, which is odd (this is the version with Brembos, police springs, 6.2 liter, and exhaust/intake).

 

[D60]

Yeah OP, you have a ground issue somewhere. I guess you could first verify ground at the vehicle side.

But if that seems ok I think EVERY trailer owner should go through their trailer wiring and eliminate all ScotchLoks. Trailer manufacturers use those like they're on a buy-one-get-twenty-free special, and they suck (ironically aka vampire connectors).

Obviously you should check all grounds under the trailer. There's probably just one ring terminal to the frame. Also check all connections to the trailer brakes if electric.

 

[Fordiesel69]

Ok so the trailer lights do DO NOT work with hitch disconnected. I also cleaned all the connections with no improvement. And three trucks later there is no difference.

 

[D60]

Ok so the trailer lights do DO NOT work with hitch disconnected. I also cleaned all the connections with no improvement. And three trucks later there is no difference.

Ok plug into a truck with a verified ground at the proper hitch pin. Backprobe or pierce as close to trailer connector as you can. If no ground is found just on the other side, the problem is in your trailer plug. Is it molded or the screw-together? Quality manufacturers use the former, but it's kinda rare.

edit: you also need to make sure the trailer manufacturer used the accepted industry standards for wire colors. I've seen some CRAZY stuff. And sometimes they'll use an RV harness if it's all they have, which is different from utility trailer/car hauler standards.

 

[Bailes1992]

The seven pin has a ground, but if that ground is "open", then the hitch system may provide a ground. Your trailer lights should work even if the trailer is not hooked up to the tow vehicle via the hitch.

View attachment 189421

Something I've never thought about before. We have different plugs over here. The 'current' standard is the 13 pin that is used accross Europe...

 

[oil pan 4]

Ok so the trailer lights do DO NOT work with hitch disconnected. I also cleaned all the connections with no improvement. And three trucks later there is no difference.

Where the ground wire actually connects to the trailer or vehicle is bad. Chances are it's just attached to the frame at some random poorly chosen spot. On the vehicle I'll run the ground up under the hood and put it with a bunch of other grounds. On the trailer side the ground just has to go somewhere it wont always get wet, not really realistic. When I wire a trailer I run actual ground wires and don't rely on grounding to the frame.
If the trailer is wired so the grounds are connected to the frame and the plug wired to a spot on the frame, every time you go to use the trailer you are going to have at least one or all of the lights not working.

 

[MNgopher]

As others have noted, likely your trailer has a ground issue. Found the same problem with a friends boat trailer - it was grounding through the ball and gave all sorts of trailer connected disconnected messages. The fix was to repair the wire harness where the wire was broken and it fixed the issue.

If I read it correctly, you've had this issue with three different trucks. All of that points to the trailer as being the issue.