Grounding a Trailer

[hunterridgefarm]

Quick question.
The lights on the trailer go in and out when hooked up to my truck. Brake light on brake box inside truck does not come on when trailer in first pluged in but will come on at times when driving down the road.

All wiring looks good. Someone mentioned that some trailers are ground through the hitch and ball and if there is rust in the hitch(coupler) this may prevent the connection. I am going to sand and scotchbrite the inside of the coupler and see if this works.

Anyone know if this is true?

 

[Dmace]

Yes, that is true.

The reason why it works after a little driving is because the trailer is bouncing up and down going down the road and it is moving around on the ball hitch. All this movement scrapes off a layer of rust and creates a good ground on the metal.
It was happening so much to my old snowmobile trailer, that I just scraped off a good spot on the trailer and put a self-tapping screw with eye-hook wire connector in the metal and then an alligator clip on the other side of the wire that I connected to a good ground on the truck. Worked like a charm!

The trailers that don't use the hitch itself as a ground are the 7-pin plugs, the 4-pin flat connectors use the hitch as an extra ground.

 

[Marlowe]

On a four prong connector the white pin is the ground. Too often the person connecting the wiring to the tow vehicle leaves the white wire disconnected depending on the ground to be made through the hitch. Of course, the white wire will have to be connected to the frame of the trailer as well as the frame of the tow vehicle for the ground to be continuous through the connector. Double check your white wire connections on both ends. This should cure any grounding problems.

Good luck with it.

Tom

 

[George2615]

I agree with Derek. If your lights are going on and off or your controller light is intermittent then you only have a ground through the hitch. Standard wiring should be as follows:

4 Pin Plug
Yellow - Left turn
Dark Green - Right turn
Brown - Tail lamps
White - Ground to trailer frame

7 Pin above colors same plus the following
Lt Green - Back up
Red - Batt. Feed
Dk Blu - Trlr. brakes

Sometimes you can have corrosion on the plug prongs too that must be cleaned.
George

 

[Bird]

Tom and Derek have it right. I've used trailers years ago that were grounded through the hitch and would not want to do it again because no matter how clean you have that ball connection you'll probably always have intermittent problems with it. Use a ground wire.

 

[hunterridgefarm]

Excellent, thanks guys!!

This was kinda blowing my mind. I thought it was ground through the plug. I checked all the connectors and took both plugs apart to check, traced all wires for breaks and connection.

I guess the problem was I did not check TBN first
/forums/images/graemlins/crazy.gif /forums/images/graemlins/grin.gif

I'll also connect a ground wire.

 

[MikeD74T]

Besides all the good information you've got already -something to consider. If your trailer has brakes the ground wire from the brakes should be at least as big as the brake supply wire & should run all the way to the battery ground. This is pretty much the case in factory installations. Almost every problem I've encountered with trailer wiring was bad grounds.
For a short term fix run jumper cables from trailer frame to vehicle frame.
Something I use when trouble shooting trailer wiring is a battery charger set on low charge for a power supply. You can test one circuit at a time without an endless supply of fuses. Usually when you can't find a problem on the trailer, ground between trailer & tow vehicle is at fault.

 

[bill18163]

Usually the white wire from plug on your vehicle(which is the ground wire) simply gets attached somewhere on the trailer tongue. Then whenever a circuit is run lets say for the brake lights, that individual circuit is grounded to the frame of the trailer. It works because the white wire from your vehicle plug is connected to the frame of the trailer which effectively grounds the whole trailer. The problem with this setup is that connections corrode. The brake lights all of a sudden don't work or maybe are not as bright as usual. This is usually because the connection to the frame for the ground wire is rusty. Could be the main connection up at the tongue or the ground connection for the individual circuit. There is a way around this but it is too expensive for the trailer mfg's. Simply run a separate ground wire for each circuit to a main ground wire which is terminated in the plug of the vehicle and now you are not using the trailer frame as a ground conductor. If everything is water tight it should last for quite a while.

 

[PineRidge]

I agree that the correct trailer connection is:

4 Pin Plug
Yellow - Left turn
Dark Green - Right turn
Brown - Tail lamps
White - Ground to trailer frame

Just want to add that I had an employee years back that always used a common 3 prong male and female electrical plug & receptacle (like on the ends of extension cords) to make his trailer electrical connection. He always relied on the hitch for the ground connection. I know it's not right but he never had a minutes problem with the trailer lighting so it was hard to convince him otherwise. I guess it proves that the right way is not always the only way. /forums/images/graemlins/crazy.gif

 

[pekabu]

On my 97 Expedition I've had some problems with the lights on the sled trailer. I was on the road so I put a wire from a bolt on the truck to the trailer and went home. No more snow so I forgot about it. Then I went to move the camper and the camper brakes are on (I wasn't pressing the truck brakes). Figured it was the brake controller so I unplugged it. Didn't help. Unplugged the 7pin connector and the trailer brakes were not on anymore. Crawled under the truck and noticed where the white wire from the 7pin connector attached to the frame was very rusty. A little grinding and a new bolt and everything worked again.