Fixing the lights on a trailer

[Chris H]

I hooked up the gooseneck a couple months ago, lights didn't work, jiggled the plug and the lights came on. 2 weeks later I couldn't get them to come on.
I plugged another trailer into the truck, and the lights worked fine so I assume the truck side is good.

I took the trailer back to the dealer where we bought it new about 15 years ago. They put a new plug on it and replaced a couple marker lights that have been broken at least 3 years. The dealer said the 'played around with the wiring until it worked'. Nothing specific was mentioned, no new wiring replaced. Everything seemed to work when I picked it up 6 weeks ago. I got it home and discovered the right turn signal was not working.

I hooked it up tonight and the only light that worked was the left flasher when the emergency flasher was on, and only when the lights were on. No marker lights worked. It has lights inside and a flood light outside, both controlled by a switch and neither worked.

Where do I start to find the problem?

 

[kenny thomas]

It's gotta be in the plug. It's cheap, change the one on the truck also.
I had to change to the bigger truck size plug to have good success. No more issues since I changed

 

[Caustic Burno]

Trailer lights nine out of ten times are plug or ground.

 

[Chris H]

I thought it was the plug when I took it to the dealer. They did a nice job of replacing the plug. The flatbed trailer has no problem with it's lights when plugged into my truck so I'm assuming my truck is fine. I did clean up the connections at the battery before I took the trailer to the dealer, and before I thought about testing another trailer.

When my husband was alive my assistance for resolving light problems was limited to standing behind the trailer and confirming which lights were working, so I'm really ignorant on fixing them. So, here come the questions:

Caustic, can I assume the plug is not the problem because it's been replaced and looks really good? Where do I start looking for the ground? It is an aluminum trailer, if that makes any difference.

 

[Chocolate Cow2]

I'm not Caustic but I just replaced a bunch of lights on my aluminum trailer. You'll need a drill with a good bit, replacement lights, just like or close to the ones currently on your trailer, rivets and rivet gun. Make sure your bit is just a tiny bit bigger than the rivets you're going to drill out. With a step ladder, drill in hand, remove the cover from your first light. Mite need a flat screw driver to help remove the lens. There will be two rivets. One of those rivets is your ground. Drill each rivet out and your old light will come loose. You'll see the wiring. I think there is just one wire. That wire and the wire on your light will need to be connected together. I twisted my wires together and wrapped with black electrical tape, then covered the tape with liquid electrical tape. Probably over kill. Line up the new light and replace with new rivets. Back down the ladder and turn on lights to check. I did several a night until I had 'em all. Be careful on the ladder.

 

[greybeard]

I'm not Caustic but I just replaced a bunch of lights on my aluminum trailer. You'll need a drill with a good bit, replacement lights, just like or close to the ones currently on your trailer, rivets and rivet gun. Make sure your bit is just a tiny bit bigger than the rivets you're going to drill out. With a step ladder, drill in hand, remove the cover from your first light. Mite need a flat screw driver to help remove the lens. There will be two rivets. One of those rivets is your ground. Drill each rivet out and your old light will come loose. You'll see the wiring. I think there is just one wire. That wire and the wire on your light will need to be connected together. I twisted my wires together and wrapped with black electrical tape, then covered the tape with liquid electrical tape. Probably over kill. Line up the new light and replace with new rivets. Back down the ladder and turn on lights to check. I did several a night until I had 'em all. Be careful on the ladder.

Good advise CC2 but I find it hard to believe that all the lights but one have simply gone bad since the last time she had it looked at 2 months ago. There's something common wrong, and I bet it's ground. Alum trailer, copper wire often means dissimilar metal corrosion and it's usually wherever the ground wire from the plug ties onto the trailer. The left emergency flasher can be working only because it can back feed thru the other half of the bulb to get ground.

 

[wbvs58]

Google a wiring diagram of the plug and see which colour wire is the ground or earth, where I come from it is the white one so might be the same, follow that and look where it is fixed to the chasis usually on the draw bar up near where you hitch up, if you disconnect it and clean and sandpaper the contact points and reattach with a bit of electrical grease, I would try that for a start.

Ken

 

[sstterry]

Caustic, can I assume the plug is not the problem because it's been replaced and looks really good? Where do I start looking for the ground? It is an aluminum trailer, if that makes any difference.

I am by no means a light or wiring expert, but the only thing I would add is that just because something "looks really good" doesn't mean it is. And don't assume it is not the plug on your truck. One trailer may fit slightly differently than the other.

 

[1982vett]

I have had a the pins on the truck side wear and not make good contact. A small flat screwdriver inserted will spread the pin some. Replace the truck plug if that gets the lights working because the fit won't stay tight. I went to LED lights and cut down on light problems due to bulb corrosion.

 

[Caustic Burno]

Caustic, can I assume the plug is not the problem because it's been replaced and looks really good? Where do I start looking for the ground? It is an aluminum trailer, if that makes any difference.

I am by no means a light or wiring expert, but the only thing I would add is that just because something "looks really good" doesn't mean it is. And don't assume it is not the plug on your truck. One trailer may fit slightly differently than the other.

Bingo neighbor routinely borrows my 26' to haul hay. Told me the other day my rear trailer light was out. I told him only on his truck works on both of mine.

 

[Brute 23]

Ill check my plug, bulbs, and clean up where the lights mount to the trailer. After that its time to just rip out the wires and run them new. Usually it wear spots in the wire from crossing thru beams and what not.

 

[Lucky]

I would guess it's a ground issue. It seems most trailers ground through the ball. Really need to have s good ground that hooks through the plug to the truck.

 

[Chocolate Cow2]

Thanks Greybeard. That's what happens when I post something at midnight. ;-) My reading retention wasn't good. Yes, in re-reading, it's got to be anything other than the lights themselves.

 

[jehosofat]

Buy a 10 dollar test light.

+ is positive (red)

- is negative (black)

Get back with us after all options are exhausted.

:lol: :lol:

 

[Chris H]

Wasps kept running me out of the head of the gooseneck, had to get more spray last night. I suspect the ground wire comes out of the wiring harness at a black box tucked in the back side of the hitch. That would fit with what Lucky said about trailers grounding through the ball.

 

[Nesikep]

If all the lights are bad, and the trailer brakes are bad, or the lights flicker when the trailer brakes are applied, that's probably a grounding issue.. If some lights are on when they aren't supposed to, turn signals work the wrong way, that's probably a ground as well..
Lights that just don't work, well, that's probably in the light or the wire to it.. yes, it can be incredibly frustrating finding what it is!

 

[JMJ Farms]

Been down this road so many times. As already stated over and over it's usually the ground. A lot of trailers ground through the ball. But it should ground without being hooked up to the truck if everything is wired correctly. If done right each light should be grounded individually to the trailer frame.

FWIW I had an issue awhile back. Trailer lights and brakes would work flawlessly for weeks on end. Then they would start flickering. Then work flawlessly. It's hard to pinpoint a problem when it's working. Finally concluded it was where the wiring harness on the truck connected to the plug on the truck. Took it apart and tinkered and tinkered. There was a rubber seal in between the two. I removed the seal, reconnected the two, and then put half a roll of black tape around the two ends. No more problems. I guess the rubber seal, even though it was factory installed, was keeping the two ends from making a constant good connection.

 

[snoopdog]

Intermittent trailer light problems are mostly a ground issue , in my experience . +1 on the test light .

 

[Chris H]

I took out the bolt where a ground was attached. It was on the hitch, attached to the wire that goes to the emergency brake. I sanded it clean, put it together and still no lights. I know my husband had a tester, I just need to find it. I think I'll call a brother or nephew, I think it's going to take someone with eyes on the problem to show me where to look.

Could a broken marker light knock out all the lights?

 

[Nesikep]

is it just the marker lights that don't work, or the the turn/brake lights not work either? What about the trailer brakes?