Question regarding grounds for trailer lights

[markhusbands]

First, I did search out a bunch of grounding threads, but couldn't really figure our my answer from what I found. So apologies if this is all addressed somewhere I missed.

Here goes.

I will have two separate electrical systems: 1) a 12v system with an 85 amp hour marine battery to power a few LEDs and small fan, and 2) the trailer lights.

There will be no shore power, and I am not worried about charging the battery off the tow vehicle at this point. I'll just trickle charge at home. So it is a very simple system. I might add portable solar later.

This weekend I got some help making my connections (soldered and liquid taped) and installing my fuse panel/ground bus for the battery system. I hooked up the battery and all the circuits (all three) were live. Awesome. When I permanently mount the battery in the tongue box I assume that I should also run a ground wire from the negative battery terminal to the frame.

Now we have the trailer lights. I have a flat four pin plug. There is a ground wire at the plug that will be mounted to the frame. Then I have two taillights and a license plate light that have positive and negative leads. I also have four running lights that have only a positive lead - evidently they ground to the skin when you screw them on (and I will have aluminum skin).

So first, can I ground the battery (assuming I should) and the four pin plug to the same bolt on the trailer tongue?

Second, I already have a ground wire that will run from my trailer hatch cooking lights (little LEDS) back to the ground bus and then to the battery and then (presumably) to the frame. Can I just tap into this with the grounds (negative leads) from the taillights and license light? Seems weird to ground the trailer light components to the battery ground but it seems like it would complete the circuit back to the frame ground from the four pin plug - but would do so through the ground bus and the battery terminal). The other way would be to run a whole separate ground wire from the taillights/license light back through the trailer roof out the front of the trailer and ground it right on the same bolt that grounds the four pin plug and the battery (presumably).

Third, for the running lights that ground to the skin, should I do something to ensure solid contact between the side skins and the frame? With a floated skin the contact seems a bit incidental, but maybe I'm overreacting.

Thanks to anyone that can help me out on this.

[bobhenry]

GROUND IS GROUND IS GROUND !

It is also the single most cause of light failure.

I used a dedicated ground for each and every light. I would highly suggest you concider hard wiring each and every fixture. Yes it is more work ,and takes more time and wire, but setting by the side of the road scratching your head as to why you have non functioning lights cuts into your time also.

[markhusbands]

Not sure how I can add a wire to the running lights I have now that have no negative lead. I can either use them or buy some others I guess.

But for the others, yes, a hard wire.

But I take it from your post that I CAN tap the taillight ground into the existing line that runs to ground bus, to battery terminal, and to frame?

Or no, you're saying "dedicated ground"...

[Socal Tom]

Not sure how I can add a wire to the running lights I have now that have no negative lead. I can either use them or buy some others I guess.

But for the others, yes, a hard wire.

But I take it from your post that I CAN tap the taillight ground into the existing line that runs to ground bus, to battery terminal, and to frame?

Or no, you're saying "dedicated ground"...

If you look close you will find that the mounting bolts for the tail lights are your "ground leads", just put a round terminal end under the nut you use to secure the tail light and run the other end to ground.
Tom

[Fyddler]

You should be able to solder a lead to a metallic portion of the light, or put a small terminal connector on it, and put it under one of the screw holes maybe?

[bobhenry]

Not sure how I can add a wire to the running lights I have now that have no negative lead.
Where you screw them on is usually a metal frame. place the dedicated ground there trapped under the screw head by using an crimp on electrical eye fitting. ( the round one )

I can either use them or buy some others I guess.

But for the others, yes, a hard wire.

But I take it from your post that I CAN tap the taillight ground into the existing line that runs to ground bus, to battery terminal, and to frame? YES


Or no, you're saying "dedicated ground"...

By dedicated ground I mean a hard wire that returns to ground where ever you want to call ground.

Remember that the lights get their power from the tow vehicle so Ground is actually the tow vehicles frameto the tow vehicle's negative battery terminal.

SO even if you return everything to the trailer frame if there is a intermittant ground thru the ball and coupler you still have blinking lights and turn signals that act crazy. Take a good sized allegator clip and actually connect the "Ground" (frame?) to the tow vehicle for a hard wired dedicated ground to the tow vehicle.

[markhusbands]

Okay, that helps a great deal, and thanks.

Here's more followup anyway. Pictures of running lights:



You can see there is a black positive wire and nothing else, so it is just grounding through the aluminum plate. Is there any reason why this can't work if it is screwed straight into the aluminum skin and the skin has contact with the trailer frame which will have the four pin ground wire bolted to it?

[markhusbands]

And about the ground-to-car thing.

The plugs have a ground wire that seems to lead from car battery to plug to trailer frame. I assume the car battery is also grounded to the car frame. So I'm not sure I understand why an additional wire between trailer frame and car frame is needed. Of course, I don't HAVE to understand, but the light HAVE to work, so...



And thanks for the help with this stuff. One of the many new things I'm figuring out to do this project.

[Shadow Catcher]

Using a ring terminal under the screw or soldering directly to the outside of the socket or some place else should be sufficient.

[Dale M.]

Not sure how I can add a wire to the running lights I have now that have no negative lead. I can either use them or buy some others I guess.

Open up light fixture, solder ( or pop rivet if aluminum) a ground lead onto the brass strip or wire or what ever to what ever grounds fixture through screw to skin, enlarge existing hole the single (power) wire goes through and poke new ground wire through hole with power wire .......

If you have any corrosion between aluminum skin and fixture its going to cause you grief.... And unless you do a dedicated bond to aluminum skin (from master ground connection on plug) its dubious the skin will have good enough ground to insure good light operation.... Just mod fixture to add dedicated ground wire (making it a two wire fixture) and life will be simpler as time goes by.... IF you are running power lead to lamps, its no more trouble the add dedicated ground wire along with it...

Dale

[bobhenry]

And about the ground-to-car thing.

The plugs have a ground wire that seems to lead from car battery to plug to trailer frame. I assume the car battery is also grounded to the car frame. So I'm not sure I understand why an additional wire between trailer frame and car frame is needed. Of course, I don't HAVE to understand, but the light HAVE to work, so...



And thanks for the help with this stuff. One of the many new things I'm figuring out to do this project.

In a kinder gentler world it wouldn't be needed. Some may even argue it is overkill but during my 2+ years at U haul a simple sliver of wire wrapped around the coupler and slammed in the trunk lock solved thousands of mysterious light maladies. Rust and galvanic corrosion already mentioned are the biggies that block a good ground thru the frames of the trailer to the tow vehicle

[markhusbands]

Okay, well, two alligator clips and a strand of wire doesn't seem burdensome, so thanks.

[markhusbands]

So, I made the decision to just buy some new LED running lights with a dedicated ground wire, and I'll just wire ALL the grounds from my taillights, running lights, and license plate lights back into the ground bus and across the battery terminal and into the frame. For $25 I'd rather keep another task from getting added the the ever-expanding to-do list. Then I'll add a bobhenrywire between the trailer frame and some part of the tow vehicle - probably the hitch bar, which is bolted to the frame.

[pchast]

I have a friend with an older Airstream. They had mild shocks from their
outside lights that were grounded through the trailer's skin.

Its cause was an intermittent ground from the corroded trailer connector and
not enough ground to compensate through the hitch.


We cleaned things up. However, this is not a recommended method for, what
seems, 'obvious' reasons.


(I don't think it was an original installation.)

[CarlLaFong]

I have a friend with an older Airstream. They had mild shocks from their
outside lights that were grounded through the trailer's skin.

Its cause was an intermittent ground from the corroded trailer connector and
not enough ground to compensate through the hitch.


We cleaned things up. However, this is not a recommended method for, what
seems, 'obvious' reasons.


(I don't think it was an original installation.)

If they were getting shocked, it wasn't from the 12 volt system. There is no way that 12 volts will produce enough current to shock someone. I would make sure the shore power on that Airstream is properly installed and grounded