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.

 

[pennwalk]

Especially on older vehicles and trailers getting a good frame ground can be a pain then when it sits out behind the barn you are liable to have to do it all over. Trailers are a pain. /forums/images/graemlins/crazy.gif The last time I went to hook up my trailer the lights didn't work and it gave me fits. I ended up using a different vehicle and later on I discovered that the converter box for the trailer lights wasn't getting good ground. /forums/images/graemlins/frown.gif Another couple of perfectly good hours wasted. /forums/images/graemlins/frown.gif

Chris

 

[755inNY]

<font color="blue"> Especially on older vehicles and trailers getting a good frame ground can be a pain then when it sits out behind the barn you are liable to have to do it all over. Trailers are a pain. </font>

I would gladly pay an extra $50 for a trailer if it offered a separate ground wire to every light (including marker lights) instead of relying on the mounting screws to make ground to the frame. What a time consuming pain in the rear to chase down bad ground connections.

Jeff

 

[BGL990]

I absolutely agree. Whenever I have to replace trailer lights, I always look for ones with separate ground wires. Even well prepared screw-into-frame ground connections will go bad over time as the screws rust.

Once or twice, where there was no separate ground wire run back to the lights, I've welded stainless steel machine screws to the frame and used those as grounding studs with wires to the lights.

 

[century3045]

I try to use self tapping screws when attaching lights to trailers. It seems they dig into the metal a bit better, even if I have to drill a pilot hole to get it started. If I do use a bolt I will use one of the washers that cut into the metal.
An old lawnmower or motorcycle battery works good for testing wires also, its light and can be used where theres no electricity.
I ran into a problem once with the tee conector harness that fits between the taillight harness on the rear of the truck. Apparently the ground wire was just bad and it was causing all kind of problems on the trailer end, such as left turn would blink on L and R , running lights would cause turn indicator in truck to come on, and such. I was just about to pull the steering wheel and replace the turn signal switch and then decided first to replace the tee connector with a new one, good thing I did. Although the turn signal switch can cause these same problems, unhooking the trailer from vehicle made the problems go away, this convinced me it wasn't in the turn signal switch.

 

[FarmDiesel]

Just a note...before you connect the white wire in a 4 wire flat plug on your tow vehicle to ground on the trailer, take a 12V test lamp and check the wire for any power with the tow vehicle in reverse.

Some vehicles are wired with that 4th wire as the reverse wire. For example, I know that if you get an aftermarket converter to add a 4pin flat plug to a 95 F-150, the white wire is reverse. Ask me how I know that one...

 

[JeffRey30747]

If you travel the interstate at night, it is easy to spot the guy who is using the hitch for the trailer ground. His trailer running lights are flickering brighter and dimmer as the trailer bounces down the road. /forums/images/graemlins/wink.gif
Whenever you wire a trailer or vehicle, save yourself some trouble later and terminate the ground wire properly on both sides.

Jeff

 

[LBrown59]

<font color="blue">An old lawnmower or motorcycle battery works good for testing wires
Something I use when trouble shooting trailer wiring is a battery charger
<font color="orange">===== </font>
<font color="#666666">Something I've used for testing automotive wireing and lights both on and off a vehicle is a model train transformer.
I have 2 of them That I've been using for that for the past 48 years.
</font>

 

[RobertN]

There are some good answers here already. I just thought I would pass on a web page that has very good info on trailer wiring, and covers the common connector types. I have found the information very helpful.

Marks RV

There's info on 7-wire RV, 4 pin flat, 6-wire round horse trailer, and brake controller info.

 

[rdln]

robert been to that site before, he is the only (maybe just the easiest) place on the web to find mobile home axle brake parts.