I have a camping trailer from 1978, and while getting ready to go on the road again I noticed the running lights are acting wonky. I think it must be a wiring issue but don't know much about electrical systems. The plug-in to the tow vehicle is newer, just a couple years old, but I think the rest of the wiring is original. My trailer is equipped with lights as follows: a yellow one on each top front corner (2 total), a yellow one on each top side corner (2 total each side), 5 red ones along the top rear, and 2 larger red rear headlights. With the tow vehicle's headlights on, all trailer running lights come on except the two red ones on either side of the center top rear light. When I first tested the left blinker, not only did the left rear headlight blink but all the lights along the top on both sides were blinking. That issue seemed to resolve itself, and now when the left blinker is on the left rear headlight and the two lights on the top left rear corner blink, which seems right to me. With the right blinker on, however, only the right rear headlight blinks (and it doesn't blink very noticeably, as the light doesn't go all the way off it only dims on the off-blink). This is not ideal but it's something I could live with if I had to. However, the real issue is, when I step on the brakes no additional trailer lights come on. I wonder if the two lights on the top rear that never come on are supposed to be the brake lights? If it were just that these aren't coming on I would replace the light fixtures to see if that resolved it, but what does happen when I brake is that the left rear headlight and two lights on the top left rear corner go out completely. All this makes me think something is up with the wiring.Does anyone have ideas about what specifically might be going on or how to address it?

Most likely a bad ground some where. Could be the running lights positive side also but I'd start checking ground connections.

First, the large red "headlights" are called tail lights. Those should have bulbs in them with 2 filaments. The dimmer filament should light up when you turn on the headlights. All of the marker lights (yellow and red) up top should also light up with the headlights. These are all fed from a single pin on the trailer plug.Next, the brighter filaments in the tail lights are for the brake and turn. With the brakes on, both tail lights should get much brighter. When you use the turn signals, the same filament should blink and only that one. None of the marker lights should flash. There is one wire for each turn signal coming from the trailer plug.Since you say other lights are flashing, I'm going to guess that your ground connection from the truck to the trailer is bad. Check for a white wire coming from the trailer plug that attaches to the frame. Without a good ground, the different circuits will share with each other through the dual filament bulbs.

On any 12 volt vehicle system, consider it a problem with a ground until proven otherwise, and check them first. :)

Thanks y'all, I found the ground wire just dangling. It had been attached to the negative terminal of my battery and when I replaced my batteries I forgot to re-attach it, d'oh! I think I'll try attaching it to the trailer frame instead of the battery terminal.

spacebetty wrote:Thanks y'all, I found the ground wire just dangling. It had been attached to the negative terminal of my battery and when I replaced my batteries I forgot to re-attach it, d'oh! I think I'll try attaching it to the trailer frame instead of the battery terminal.Seems like the right answer. You may want to tow the trailer without a battery installed and you'd want the lights to work.

RV trailer running lights wiring issue | Good Sam Community

14 Replies

spacebetty
Explorer
May 19, 2015
I suppose the only answer is that the wire connected to the negative battery terminal must be grounding the entire electrical system. Yikes!
spacebetty
Explorer
May 19, 2015
The battery negative lead doesn't go to the frame, it runs up into a panel under the trailer and gets bundled with a bunch of other white wires:

Yes, I realize there is a burned-out wire in this picture, it was taken a while ago and the wire was fixed. It's mosquito hell out there right now, so I didn't want to unbolt that panel again to get a new picture.

The only wire bolted to the frame in the vicinity of the batteries/plug is the one I was messing with, which I have now cut from the bolt, and still nothing is affected. I'll probably drill a new hole in the frame to attach that wire to even though it appears to be useless... you never know. In the meantime, the only other things I've seen attached to the frame anywhere are:

This solid metal uncoated "wire" that isn't electrical, which comes out under where the hot water heater is

And this wire of indeterminate color that comes out under the door on the rear of the trailer

Sorry for the poor picture quality.
DrewE
Explorer II
May 19, 2015
It looks like you were trying to link pictures to your personal gmail inbox. Be glad random people don't have access to it.

If you have some space between the nut and the frame/connector, maybe you can just cut the rusty bolt in half with a hacksaw or a dremel and cut-off wheel or whatever.

You want the ground connected securely to the frame. Rather than attaching it to the battery terminal, maybe you can attach it to the other end of the battery negative lead (assuming it just runs a short ways and goes to the frame). I think the fewer wires attaching to the battery the better, if only to reduce confusion in the future.
spacebetty
Explorer
May 19, 2015
Oh, I guess my photo posting didn't work :/
spacebetty
Explorer
May 19, 2015
Thanks for that, BFL13!

I have several new questions :/ Should've known this wouldn't be as easy as all that!

So what I thought was the ground wire was attached to a bolt on the underside of a trailer rail, and that whole assembly was just a mess of rust. I started cleaning it up but it was too far gone, so I thought I'd take it off, get a replacement bolt/nut, replace the ring connector, and possibly grind down the area around the hole in the frame (is that necessary? wire brush doesn't do much good). But I can't get the nut all the way off...

It would be no problem if I could get better leverage on top; the head of that bolt is a flathead and it's rusted away enough that the edges are a bit rounded, and I only have space to use one of those little horizontal ratchet drivers...

So, is it a bad idea for any reason to extend the wire a bit and connect that ground to my battery? The other option sounds like hard work, esp without access to a lift... I don't even know if I'd want to use a grinder in a space that constricted/position that awkward.

Oh, also, everything (incl. everything inside the trailer) is still working exactly how it had been before I started loosening that connection - could it still be acting like a poor ground even in that position (and coated with WD40)? Or does that mean this isn't even the ground wire for the running lights? I mean, clearly it needs to be fixed regardless.

Would there be a ground for the running lights on the truck as well as the trailer, or only on one or the other?

A few years back when I had the hitch wiring installed on my truck, they replaced the trailer cord as well, so that wiring is also newer.
BFL13
Explorer II
May 15, 2015
spacebetty
Explorer
May 15, 2015
BFL13 wrote:
wnjj wrote:
spacebetty wrote:
Thanks y'all, I found the ground wire just dangling. It had been attached to the negative terminal of my battery and when I replaced my batteries I forgot to re-attach it, d'oh! I think I'll try attaching it to the trailer frame instead of the battery terminal.

Seems like the right answer. You may want to tow the trailer without a battery installed and you'd want the lights to work.

Against THE LAW regarding break-away brakes for battery power to the brakes.

Oh shoot. Your comment made me realize the wire I thought was ground is probably actually going to the breakaway brakes. I was wondering why it came out of a little box on the tongue rather than from up under the trailer where the rest of the wires come out :/ I didn't even realize the breakaway breaks were connected to the battery, but that makes total sense. Also, earlier today I had been second-guessing my memory that it was connected to the negative terminal, I thought I actually remembered positive but I dismissed the thought as nonsensical. The wiring on this thing is soooooo shady, even if I knew what I was doing I think I'd still be confused haha! Guess I'll have to take another look at everything tomorrow.
BFL13
Explorer II
May 15, 2015
wnjj wrote:
spacebetty wrote:
Thanks y'all, I found the ground wire just dangling. It had been attached to the negative terminal of my battery and when I replaced my batteries I forgot to re-attach it, d'oh! I think I'll try attaching it to the trailer frame instead of the battery terminal.

Seems like the right answer. You may want to tow the trailer without a battery installed and you'd want the lights to work.

Against THE LAW regarding break-away brakes for battery power to the brakes.
BFL13
Explorer II
May 15, 2015
Our 1981 truck camper we just fixed up had an "issue" with the clearance lights where rear rights on the right side would not work but the left side's did.

Much chasing around pos and neg, no joy. Eventually, I just jumpered the left to the right back clearance lights externally, so now they all work.

I never found the actual fault, but at least we can go RVing in the thing now! :)
wnjj
Explorer II
May 14, 2015
spacebetty wrote:
Thanks y'all, I found the ground wire just dangling. It had been attached to the negative terminal of my battery and when I replaced my batteries I forgot to re-attach it, d'oh! I think I'll try attaching it to the trailer frame instead of the battery terminal.

Seems like the right answer. You may want to tow the trailer without a battery installed and you'd want the lights to work.