True Ground?

I was installing a new set of trailer lights on my project this weekend and when I would press on the brake the lights would turn off, also the blinkers would blink on all the trailer lights. I figure it is a grounding issue, so here are some questions...

Does the trailer have to be attached to the vehicle to create a ground?

What constitutes as a true ground? Could I put the ground wire on a negative terminal of a spare battery to double check that it is indeed a grounding issue?

How can I check if the ground is properly set with a volt meter?

Re: True Ground?

The light harness between the trailer and the vehicle should have a ground wire in it. If your lights are behaving like they are, one side of that ground is bad. You don't want to rely on a ground between the trailer and the vehicle through the hitch.

As far as the ground on a spare battery, not sure what you are talking about.

You could possibly measure betweem the vehicle and the trailer with a meter set on a low ohms scale but even a bad ground is going to have a fairly low reading.

Also make sure that the place where the light mounts on the trailer has had the metal ground down to bare metal.

Re: True Ground?

If it was working before and started doing that then yes it most likely is.

es the trailer have to be attached to the vehicle to create a ground?

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No it doesn't, my personal preference is not to have the trailer hooked up when installing lights, just the harness plugged in. The reason being is the white wire is the electric connection to ground on the truck and trailer and in the trailer unhooked condition it tests it and is a common point to lose ground connection.

How can I check if the ground is properly set with a volt meter?

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With the scale set to Rx1 put one probe on a clean connection spot on the trailer and the other probe goes to the white wire in the plug in connector. It should read close to 0 ohms. That tests the main frame ground on the trailer and do the same on the one going to the truck to bare metal it should be the same. Each light set has its own frame ground once you have a ground reading you can move the probe from the frame metal contact point to each of the colored wires while holding the other on the white wire and you should get a reading if the bulb element and ground path are intact and it wont be at 0. You should get a impedance reading. This is for conventional bulbs , not sure what reading it will be on a LED types.



And right off hand I would suspect it is the main ground at trailer or truck end.

Re: True Ground?

I do have a ground wire coming from the trailer harness about 9" long. I drilled a hole and attached it to the trailer with a screw.

My question about the battery is instead of "testing" several different areas on rust free space on the vehicle or trailer is there a way to KNOW what would be a ground?

Re: True Ground?

I you have a welded together trailer, your entire trailer is the ground. If it is a bolted together trailer all bets are off.

As a test, get a large jumper cable and connect it between the frame of the vehicle and a bare metal spot on the trailer. If that fixes your problem, you have a ground issuue through the harness.

Re: True Ground?

One mounting screw on each light set is hooked to the ground for that set when mounted it makes contact with the frame and makes up the return ground path. You can run a extra wire from that mounting screw to the plug ground white wire and many do just that.

Re: True Ground?

scrit9mm said:

I do have a ground wire coming from the trailer harness about 9" long. I drilled a hole and attached it to the trailer with a screw.

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This has to be down to bare metal where this attaches.

Re: True Ground?

In addition to all that's said, the - terminal of the battery is "true ground" in your vehicle. You asked the question, that's the answer.

So the question really should be "do I have true ground connected to where my white wire connects to my tow vehicle and do my lights enjoy the same luxury"....beins their ground is accomplished as mentioned above?

HTH,

Mark

Re: True Ground?

bruceb58 said:

This has to be down to bare metal where this attaches.

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wouldnt it be to bare metal because I drilled through the frame rail? The screw will be in contact with the un-coated metal in the hole.

Re: True Ground?

The kit is a sealed unit. there is only 5 wires coming from the harness.

White> ground

Brown> Left
Yellow

Brown> Right
Green

Re: True Ground?

What makes me believe that this is a grounding wire issue at the trailer is that everything works properly on my other trailer.

Re: True Ground?

scrit9mm said:

wouldnt it be to bare metal because I drilled through the frame rail? The screw will be in contact with the un-coated metal in the hole.

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Assuming its a sheet metal screw, yes. Did you attach a ring connector to the end of the wire? Is it a good crimped or soldered connection as well?

Re: True Ground?

wouldnt it be to bare metal because I drilled through the frame rail? The screw will be in contact with the un-coated metal in the hole.

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not nessaraly clean the paint/rust around the drilled hole about 1/2 inch , then you know for sure it is.

Re: True Ground?

It is a ring connector with a crimped connection.

Re: True Ground?

I'll try that Hawker.
Thanks.

Re: True Ground?

scrit9mm said:

... What constitutes as a true ground? Could I put the ground wire on a negative terminal of a spare battery to double check that it is indeed a grounding issue?

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It sounds like you are attempting to use a spare battery as a sort of portable ground.
Kind of like the mythical "Skyhook", but the other way around. No, that will not work.
There is no such thing as a "True Ground?. All grounds are relative.
The ground on your trailer is at a different potential from the tow vehicle until you hook them together electrically.
Same thing goes with your Boat, Generator, the Earth, Airplane, you name it.
By the way, it is called "Ground" because it refers to the electrical potential of the ground, literally the planet Earth. Measured from a ground rod buried deep!
So, obviously, your trailer is not technically grounded as you go down the road. But the trailer and tow vehicle are grounded together.
I hope that clears the mud!

scrit9mm said:

... wouldn?t it be to bare metal because I drilled through the frame rail? The screw will be in contact with the un-coated metal in the hole.

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Yes, for a while.
It is bad engineering practice to use the hardware to conduct the power.
The voltage, the dissimilar metals, and a drop of water, will form corrosion in a short time.
Steel on steel is an example of dissimilar metals unless they are identical alloys forged from the same pouring.
The Screw and the frame are definitely dissimilar metals.
Your best bet is to clean down to bare metal around the screw, and coat the trailer and the wire lug in a little grease for protection.
Many people will say this is overkill. And this is also why so many lighting problems have a grounding issue at the end of the story.

Re: True Ground?

MH Hawker said:

No it doesn't, my personal preference is not to have the trailer hooked up when installing lights, just the harness plugged in. The reason being is the white wire is the electric connection to ground on the truck and trailer and in the trailer unhooked condition it tests it and is a common point to lose ground connection.

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I've seen plenty of trailers wired that didn't use the white ground wire. I've even seen OEM trailer wiring harnesses that don't bring out a white wire at all, they completely disregard the ground. In other words, its entirely possible the trailer DOES require a hitch connection.

(no, i'm not saying that is a good idea, and i've redone every one I've owned that had that, but they do exist.)

Re: True Ground?

I have never seen an OEM trailer that is missing the ground wire.

Re: True Ground?

UncleWillie said:

It sounds like you are attempting to use a spare battery as a sort of portable ground.

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I was going to use the battery to test the ground, not have it as a permanent solution.

Re: True Ground?

scrit9mm said:

I was going to use the battery to test the ground, not have it as a permanent solution.

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You mean connect the negative terminal of the battery to negative terminal of the harness and positive leads to the plug terminals for the various lights right?