When i hook up any trailer, none of the lights on the trailer will work.

 

Add a ground wire from the trailer frame to the truck frame. Also make sure that the grounds for each light are rust free.

 

Thank you. Which wire is the ground foe the lights, and are you referring to the trailer lights or truck lights? thanx again.

 

Usually, the trailer is grounded through the hitch and ball. I have found that an extra wire from the trailer to the tow vehicle helps. It can be a simple wire with an alligator clip on each end from trailer frame to tow vehicle frame or wire up a permanent wire on each end with a coupler. You might have a ground wire already in your wiring coupler. You should have two wires for each tail light on the trailer. If you look at the back of the light, you should see three wires. One is turn/stop an other is the night time light and the third should be the ground. On my trailer, the white is the ground and it goes to the frame next to the light. The frame of my trailer is aluminum so it is connected to the hitch with a steel coupler which causes a loss of connection with the ground circuit. I use a separate ground wire from the aluminum frame to my connector to get past the steel connection. You don't show what you are towing with or what type of plug you are using.
If you have a regular jumper cable, connect it to your tow veh frame and the trailer frame. That will rule out a ground issue.

 

You should never rely on the hitch and ball to complete the ground for a trailer.

 

 

 

It is vey easy for verify a grounding problem with a trailer. Take a jumper cable and make a good connection between the trailer frame and the frame of your truck. If the problem goes away, it is a grounding issue, and the jumper cable forms a new ground.

The seven pin connection should do the grounding as noted in the diagram above. Until more recently, the Ford trucks typically loose their ground at the seven pin because the grounding pin is lowest on the plug and is an easy target for corrosion.

Steve

 

Moved to the towing forums.

 

That jumper will not fix a ground problem that exists at the lights.

As in, some lights ground at the mounting studs of the lights.

You can have a solid ground connection from frame of vehicle to truck plug, then from trailer plug to trailer frame.

Then, loose that ground through pivot points on tiltbed trailers etc or plain corrosion or lack of a solid ground connection at the actual lights.

Hope this helps someone down the line.

And as said every plug has a ground pin for a reason. Dont rely on the ball to carry the ground.

 

That jumper replaces only the white lead from truck to trailer. There is a redundancy in the connection as it is all tied together at the J-box, which in turn is connected to the trailer frame at some point, so you are looping back to J-box then to the grounds for the lights.

You are not trying to jump to the lights via the frame, only to the common connection. In other words, the ground in the seven pin cord runs to the J-box, which has multiple connections, one or more of which ground to the frame at some point, so jumping replaces only the section of wire in the seven pin cord.

I haven't seen a case in which grounding the frame doesn't feed back at multiple points. I guess there might be exceptions. The reason the hitch ground historically is still so often suggested is it does actually work in many cases. That is also the reason, in the diagram above, it shows a ground connection to the frame. That is pretty typical of trailer wiring diagrams. At least in RVs, there are multiple feedback loops for the ground.

Although it is very hard to tell it, in the graphic I posted last night of the J-box in this same section of the forum, the wire nut capturing the grounds actually has five or six leads running into it, one of which ultimately goes to the frame.

Steve

 

I think we agree. But not all lights have a ground wire going to them.

In that case they ground is via the mounting points being the studs of the lights, or mounting screws or bolts.

Think of the clearance lights that every stinking horse trailer uses that have the ground strap for the bulb ran under a pop rivet that anchors the light to the trailer. They don't bite into the metal of the trailer very well and commonly I can smack that rivet with a punch and the light will come on.

You can have a perfectly wired and grounded tow vehicle and a good connection in the 7 way trailer end with a good ground to the frame and that ground can get lost at the pop rivet therefore that clearance light won't work.

Additional jumper ground wires from the trailer to the truck won't fix that.

Hopefully I explained that well.

I see it all the time with horse / utility / flatbeds. Possibly in the RV industry each light has a ground wire going to it.

I do tons of axle / brake work on travel trailers but nothing on the interior side.

 

Yes, we do agree. My initial suggestion regarding the use of a jumper was only to address a small part of the puzzle. I actually do not use jumpers. My Flukes are my most essential tools.

Appreciate you input. I work on horse trailers only very rarely and anything other than RVs almost never.

One thing I am seeing it that although the problem often is a ground between truck and trailer, I am finding folks now are jumping to that as an explanation for almost every problem, even when the existence of a ground is obvious given they will have other components operative that depend on that same ground.

I like working with electricity as it is one of the only things that is truly challenging in my work.

Steve

 

I totally agree, and

It's "never just a bulb" lol

 

While working on school buses I've found sometimes just the ground screw on the light socket has rusted just enough so it doesn't light. Replaced with stainless screw. Over the years I've not had those come back. The socket rusts out instead.