crazy trailer light problem

[muddstopper]

Got a head scratcher with my trailer lights. My tag along trailer I use to haul everything set unused for 2 years. It was loaded down with metal building studs and I just got around to selling them a few weeks ago. The taillights where broken and not working so I bought new lights and installed. Hooked trailer to truck and no lights worked. Well my first thoughts was corrosion in the plug or bad ground. I took the pigtail apart, cleaned all the wires and tested the lights using a battery charge, everything worked. OK plugged it into truck and nothing worked. So next was pull out the meter and check outlet, everything seemed to be working but it was crusty so I took the outlet apart, cleaned all the wire ends and reinstalled. Meter said everything worked. Plugged it all back together and still no trailer lights. Almost automatically thought bad ground so I took my meter and did a continuity check between the outlet and the trailer, meter beeps so ground is working. I tried bumping the plug in to make sure it was getting contact, wiggled and pulled on the plug, nothing. Well crap, sometimes I have had trailer lights not work until the trailer was pulled cleaning up the ball and coupling making a ground and then the lights would work. Not this time. I loaded my tractor and pulled the trailer about 5 or 6 miles and back, still no lights. What am I missing.

 

[Del_]

It sounds like the plug is not making good contact between the male and female connections.

 

[capetrees]

Are the lights grounded to the frame as a result of the nut/bolts that attach them to the trailer? Corrosion there can play a part.

 

[husky455rancher]

I would start by making sure you have really good grounds. I’ve seen crappy ground contacts do wacky things.

 

[skeet88]

It will be extra work but run a separate ground wire to the lights from the pigtail to bypass the frame ground .

 

[Aknutter]

What is the make and model of tow vehicle?

 

[Aknutter]

A test light or one of these.

On the 2000 + Ford F-250 check the fuse box under the hood, they have separate fuses for the trailer lights circuits

 

[cookies]

When it comes to trailers the plugs get worn out, they simply wear from vibration+ electricity eats away the plating, pits the connectors at the contact points and the tension is lost in female terminals. The truck connector is often the issue as its the most used, it may work on other trailers with newer connectors but a older more worn one fails and having it hang will make it worse.

 

[Bearcreek]

I never rely on the chassis ground. Everything gets ground wires run to it. I'd start with that, assuming the truck end has tested good for sure.

 

[JRM]

Eliminate the tow vehicle by plugging into another trailer. Or plug another vehicle into the problem trailer. At least narrows down the problem.

 

[lwmibc]

From an old logging truck driver--any others of you out there that drove know you fix trailer lights a lot, sometimes more than once a day. 'One of the jobs of a log loader operator is to find anything vulnerable on the truck and break it off just to remind you'.

First--there's no magic; no light, no current path; either positive or ground (assuming the bulb filament is good). If no lights work= bad ground, somewhere. Find it and fix it. Note that ground has to go through the plugs, the trailer ball won't do it.

I'll assume normal 7-wire RV trailer plugs, so here's what I would do. First, get if you don't have one a plug-in test plug that you can plug into the vehicle receptacle; that tells you if you're getting correct power on all circuits that far.

Second, install one of those black connection boxes like this one--

https://www.napaonline.com/en/p/GRO821000
--somewhere on the front of the trailer, and run the cord from the male trailer plug to one of these boxes. Then you'll be able to determine with a test light that you're getting power that far, one circuit at a time.

Make all individual light connections then to that box. Then for each light that doesn't work, you have just the one circuit to trace.

The key is to make it easy on yourself to find a problem. Trailer wiring is incredibly simple; if there's a rat's nest in there now tear it all out and start over, doing it right. Life is too short to do anything less.

Now, that advice was free so rate its value accordingly. I drag at least 4 trailers around with a pickup now that I'm retired, up to a 3-axle goose-neck equipment trailer--and all the lights work. There's nothing magic in making trailer lights work.

Note that a test meter giving a beep will do that with just a few milliamps of current flow, where the filament on the lights will need amps if incandescent. Continuity indicated by such a meter's audible sound may not be enough to run the light.

 

[Husky Man]

What style plug are you using mudd?

 

[Abbeville TSI]

Test lights and beeping continuity meters are not the choice of pros. Always check voltage! This is from a former police equipment installation tech for the state police.

 

[Okie]

read what lwmbic says a couple of times.

A beeping test meter cannot be trusted.

You can trust the Hi-way patrol when he pulls you over. He might even help you get your trailer and vec towed to a shop that can fix the lights.

I keep brake light assembly that I removed from an old vec with alligator clips on the 3 foot long wires and a ice pick for probing and it's hanging in the shop on a peg board readily available and I use that instead of a voltmeter. It places a AMPERAGE load on the vec/trailer wiring wiring just like the trailer lights. I also run hard grounds to my trailers. Ground through the frames and trailer ball is no good.

I can reliably troubleshoot faster with my homemade brake lamp assembly instead of using a meter.
I'm also a electronic tech and Journeyman electrician and have several expensive electrical testers but the vec brake lamp assembly test method is more reliable than using voltmeter.

 

[lwmibc]

In response to Abbeville--I have to respectfully disagree with the voltmeter if used without load; the input resistance of a digital voltmeter is so high that a poor connection can supply enough current to result in a satisfactory voltage reading that could still get dragged to zero when an incandescent filament is connected. I still prefer an incandescent test light; if it's bright the light will be bright if connected where you're testing.

But for the OP--it will be simple and you'll find it, trailer wiring is not difficult to master. No rocket science in it anywhere--not even an O-ring. (And then I have to remember that the Challenger explosion might be before a lot of people were born!--holy crap where did the years go...). Musta been having fun; after all, got 15 chain saws.

 

[ChasSC]

I second Capetrees comment.
Remove the lights and clean the ground contacts, both sides where the lights mount and where the bolts make contact. You can run an external wire from your ground to the lights to check it first.
If you are installing LEDS I always run a separate ground wire to each light.
I use both a meter and a 12v test light.

 

[skeet88]

And then I have to remember that the Challenger explosion might be before a lot of people were born!--holy crap where did the years go...).

I was outside after lunch in 10th grade,we could see the smoke trail from school in southwest Georgia.Strange how one can remember where they were at times like this but for the life of me I couldn’t tell you what color shirt I wore the other day.

 

[muddstopper]

Lots of good suggestions. I do have a ground wire from the trailer receptacle to the trailer. My experience has shown 99% of time, Poor ground is the likely problem. The trailer plug was checked and cleaned and all connections double checked. I cleaned the light mounts using a wire wheel on a grinder and made them shiney when I installed the new lights. I dismantled the receptacle and cleaned all the wires and made sure they where tight. The one thing I didnt check was the actual contacts of the plug or receptacle. Usually a wiggle or unplug and re-plug will polish them up enough to work, even if it is temporary. The trailer is still hooked to the truck, I plan on pulling it back up to the shop and having another go at it. I still think its a ground problem and I plan on checking the wires running back to the lights. I did run wire a ground wire all the way to the light fixtures when I built the trailer and it could be its broke somewhere between the tongue and the tail lights. The question was asked what kind of plug am I using, it is a 7 flat prong rv type. It also has the built in 4 or 5 pin flat plug. I like the ideal of one of those test plugs, I will have to try and find one. I also made trailer connections inside a water tight electrical box mounted in the tongue. I havent taken the cover off yet to see if the problem could be there, but all lights work when hooked to a 12v power source at the plug, so I dont think the problem is there. I know its something simple, just got to find it.

 

[Okie]

I also keep a 3oz tube of Dielectric grease (silcone grease) close by when I'm fooling around with the auto light sockets and trailer/lawn tractor electrical plugs. Amazon and most any auto store will have such, permatex is a good name brand, sometimes called bulb grease. Just kinda watch the price, some is over priced and a little bit goes a long way when using.
It's also really good to smear little bit onto screw in light bulb bases to keep them from sticking in their sockets, especially if it's a outdoor bulb.

It's main purpose is just as a shield so as to keep air/moisture away so as to prevent corrosion.
It does not directly aid in conductivity of the electrical male/female connections.

 

[CatMan Fetters]

I had a similar problem and it was the ground wire that still was totally enclosed in it’s sheath ,the copper wire inside was totally deteriorated 3 foot in, replaced the whole ground wire from front to back, issue solved.