Intermittent problem with trailer brake light

[Vecchio]

I have a very strange problem with the passenger side lights on my trailer, in that sometimes they work, sometimes they don't. I have a second truck that I hook up and it works every time. The real weird thing is I have a tester and when I hook it up to the problem vehicle it lights up for everything, and shows no problems. Most of the time when I first hook up the trailer it won't work, but if I then turn on the truck and re-attach the connector it starts working just fine. I thought the problem was with the truck, but the tester shows every function working every time. That means it must be in the trailer, but then why does it work with my other truck? It is a perplexing problem and it is driving me nuts. Does anyone have any ideas for me? I have tried re-grounding both the connections in the truck and on the trailer, and that hasn't helped. I changed the plug on the trailer side, and the plug in the truck is brand new as well. Is it possible that my battery in the truck is weak, and causing the problem with my brake light, and then when I start it and the alternator adds some juice it gets enough power to function? Any help would be greatly appreciated.

 

[Grandad]

Electrical problems that aren't consistently repeatable can be a bear to fix. It certainly sounds like a loose connection somewhere. I would suspect the plugs but you've changed those, so here's what I would do. I'd determine which wires provide power to the troublesome lights on both the trailer side and on the truck side of the plugs. I'd bare a small spot on each where a voltmeter could be used for testing and then I'd try to create the same "failure to communicate" with everything plugged in. Then, without disturbing the plugs, try testing on both the truck wires and the trailer wires to determine if either side is functional. It'd at least get you started in the right direction. - Grandad

 

[gm280]

Sounds like the trailer plug could be the issue. When you plug the trailer into the first truck, the fit may be suspect with the pins socket to that side of the trailer and that is the reason it works some times and not others. But when you plug that same trailer into another vehicle, that fit is tighter and no problem exists. So I suspect the trailer plug being the problem. You could squeeze the pins on the trailer plug a little making them buldge out some to see if that fixes the problem. It wouldn't take much, so go easy with the squeezing effort. JMHO

 

[dsinger1211]

It does sound like a trailer side wiring problem however, are the contacts dirty on either plug side?? my Dodge does that between different trailers and it is due to me not keeping the dust cover closed when not in use along with the fact that it needs to have a good cleaning and then a little electrical "grease" added to ensure a proper connection

 

[Vecchio]

Sounds like the trailer plug could be the issue. When you plug the trailer into the first truck, the fit may be suspect with the pins socket to that side of the trailer and that is the reason it works some times and not others. But when you plug that same trailer into another vehicle, that fit is tighter and no problem exists. So I suspect the trailer plug being the problem. You could squeeze the pins on the trailer plug a little making them buldge out some to see if that fixes the problem. It wouldn't take much, so go easy with the squeezing effort. JMHO

I was thinking the same thing so I changed the plug on the trailer not once but twice. Both the plugs on the trailer and truck are brand new. I woold have guessed it was the trailer wiring, but you would think the same problem would occur on the 2nd truck. Another problem is once it is working nothing I do recreates the problem, so at that point testing becomes impossible.

 

[poconojoe]

Can you try hooking each truck to another trailer? Perhaps a friends trailer.
When you said " The tester shows every function", I suspect you are using one of those plug-in diagnostic devices specifically made for trailer wiring? If not, maybe one of those might help. They don't cost much and they test both sides. iboats has them under $10.

 

[1976Galaxie302]

LED or Incandescent on trailer?

If I read correctly this only happens on 1 of your 2 trucks? What year make and model is this truck?

I been building and repairing trailers for 20 years so I hope I can help get you back to having everything work.

 

[Vecchio]

LED or Incandescent on trailer?

If I read correctly this only happens on 1 of your 2 trucks? What year make and model is this truck?

I been building and repairing trailers for 20 years so I hope I can help get you back to having everything work.

Incandescent and it is a 2006 Jeep Liberty. I am really starting to think it has to do with lack of power.

 

[Vecchio]

So this is perfect example of just how odd this problem is. I just went out and hooked my trailer up to the Jeep, and the passenger side light weren't working, so I just unplugged the trailer and plugged in the little tester I bought and it showed that all the lines were working. I then plugged the trailer back in and the lights worked. I don't get t, but it almost seems like it doesn't work at first each time, I have to unplug it and plug it back in, and then most of the times it starts working again. I am at a lost, what could be causing this?

 

[gm280]

So this is perfect example of just how odd this problem is. I just went out and hooked my trailer up to the Jeep, and the passenger side light weren't working, so I just unplugged the trailer and plugged in the little tester I bought and it showed that all the lines were working. I then plugged the trailer back in and the lights worked. I don't get t, but it almost seems like it doesn't work at first each time, I have to unplug it and plug it back in, and then most of the times it starts working again. I am at a lost, what could be causing this?

I can understand your frustration. When you use your tester, I am betting it is an LED tester and not an incandescent type. And it take so little to light a LED. I would go to every light and verify a good clean ground connection. I know it eventually works, but I would clean the grounds anyway so there is not resistive ground with any of them. And if you are using the trailer are your ground point,I would absolutely remove and clean that to shiny metal. Then see how it works. Post your results after doing that.

 

[Grub54891]

Does the jeep have a converter for the lights? Sometimes they do strange things.....

 

[GA_Boater]

Does the jeep have a converter for the lights? Sometimes they do strange things.....

Eggsakly. Unplugging and replugging - Are you doing that with the lights on or off?

 

[Vecchio]

Eggsakly. Unplugging and replugging - Are you doing that with the lights on or off?

​Yeah I do have a convertor box. The jeep didn't originally have a tow package, and on was installed from parts from etrailer. When I unplug and plug the trailer back in the lights are off.

 

[1976Galaxie302]

Converter boxes are known to go out cause problems like you describe with random problems.

get a new converter box but this time get a powered one. It uses power from the battery to activate all trailer functions, not power from the tail lights