It's ALWAYS trailer wiring

Steve in VA · Sep 4, 2016

I hope someone can educate me on this one. I frequently borrow a buddy's 16' BP w/o brakes. So I hooked up today and about 1/2 of the lights didn't work. I figure I'll fix this for him before it comes back. Not being all that confident of trailer wiring, I start by verifying the wiring on both plugs on my Dodge. The plugs and controller were installed by a reputable dealer and I have no issues whatsoever when connected to my dump w/ brakes.

Here's the thing. When I check the male connectors on the Dodge, the right turn signal appears to have reversed polarity. By that I mean that the VOM needle moves into the negative range when that lamp flashes. The left signal, running lamps, and 12v constant reflect positive scale movement. I haven't checked the brakes yet.

How is this possible? Is there a controller issues?

Thanks in advance guys. I know I'll learn something on this one.

old · Sep 4, 2016

A poor ground will cause that because it tries to get a ground form any place it can and some times that means from the other bulbs etc.

BushogPapa · Sep 4, 2016

I replaced all my trailer lights with LEDs and I guess since they draw so little power, they never NEED much of a ground...

Has eliminated all my light problems so far...

Ron.

notjustair · Sep 4, 2016

Without a doubt, I will tell you that there are little trolls that live under my house that delight in busting trailer wiring while it sits unused. They start by rusting the ground up so it only works halfway like it should and then randomly make bulbs loose in their sockets. I'm going to kill them off someday and regain about a week of my life every year.

Ground. Check the ground.

Donald Lehman · Sep 4, 2016

The contractor supply place I worked for had 3 trailers. Most of the lights were on the blink most of the time. They were all cobb jobs. I ended up completely re-wiring two of them before I left. But one of the guys told me that within a year the road salt had both of them all messed up again. Trailer lights are a never ending nightmare.

JoeM(GA) · Sep 4, 2016

+1 poor ground

Steve in VA · Sep 4, 2016

sage advice. first line of attack tomorrow is ensure the ground wire is solidly landed.
Thanks guys.

John T · Sep 4, 2016

Having owned, used, and bought and sold a ton of trailers for nearly fifty years, I can tell you this from EXPERIENCE:

THE MOST COMMON CAUSE OF TRAILER LIGHTS NOT WORKING OR DIMMING OR MORE THEN ONE COMING ON OR OFF IS A BAD GROUND. If the ground return is bad current will seek a path everywhere else is the problem.

On my tow vehicles female outlet/receptacle I run a ground wire from it all the way up to the battery negative post versus relying on a terminal or ground wire etc back at the rear of the vehicle.

The connections are best if the terminals are crimped then soldered then covered with heat shrink tubing.

Those push on or scotch lock crimp terminals and splices always go bad lol that's why crimped and soldered then heat shrink tubing is required.

John T

Steve in VA · Sep 4, 2016

John, everything you say makes perfect sense to me, but I haven't even gotten to the trailer. The issue I described is on the male connectors on the truck. Still a ground issue? Both the bumper mounted and bed mounted sockets demonstrate the same behavior.

gtractorfan · Sep 4, 2016

Same here, constant battle keeping the trailer lights working. I saw or heard mention of "wireless tow lights". Has anyone used them? Do they include constant running lights for night driving? How would the batteries in those keep up for a long haul?

MT RON · Sep 4, 2016

One big problem is Joe Blow wires everything to his own specs and does not have a clue there is a wiring code.

Bob Harvey · Sep 4, 2016

As below - faulty ground. Does your connector (truck end) have a solid ground - might check that out. I haven't had a trailer for a few years, BUT, when I wired the last one, I used Marine multi strand cable (color coded) and shrink wrapped ALL the connections, AND put Vaseline on anything exposed. HTH

Steve@Advance · Sep 4, 2016

The modern vehicles do have some complex controls regarding trailer lights! This came about when the turn signal lamps were separated from the brake lights, and further complicated by the mfg deciding everything has to go through as many "modules" as possible! LOL

A couple of easy tests... (I prefer a test light over a VOM because it puts s slight load on the circuit, simulating what the trailer lights will do.) Try connecting test light from the right turn terminal to the ground terminal. If it doesn't work, try testing from the right turn terminal to a known good bare metal frame ground. If it works there, there is a bad ground connection to the back of the plug.

If it does the same going to external ground, pull both plugs out so you can see the back side. Those are notorious for corroding the terminals, both loosing connection and bridging across with conductive corrosion. There are plugs with the lead wires potted in, I prefer those over the screw terminal type.

Some of the newer tow packages use multiple fuses, a fuse for every circuit to the trailer. Be sure they are all good, especially after plugging into a strange trailer.

John T · Sep 4, 2016

Id "guess" it may not actually be negative/reverse voltage but just a drastic drop ??? If voltage drops drastic when a load is applied there must be a bad/loose/resistive connection from the source to that receptacle/outlet causing a V = I x R voltage drop you see in your meter etc HOWEVER a volt meter is an extremely high resistance low current draw which shouldn't cause such a high V = I x R drop in the supply circuit. The receptacle/outlet other terminals use the same ground so if its ONLY one terminal exhibiting that it don't sound like a ground problem, but hey still a bad ground can cause all sorts of weird problems????????

Still to be safe Id try a new direct dedicated circuit from the receptacle ground terminal up to the battery - and see what happens.

John T Bad grounds can be weird grrrrrrrrrrrrrrr

Oregon Tractor Jack · Sep 4, 2016

What type of Dodge and the year? The newer Dodges have all the wiring in place. All you have to do is find the connector under the dash and plug in the controller. There really isn't any way for the wiring to get reversed. If this is an older Dodge, then it does sound like the one turn signal wire is reversed. As already stated, bad grounds will drive you crazy. Strange things happen, lights light that shouldn't and others will glow dimly. In the past I have fought that on one of my trailers. The lights would work perfect in the drive way. Pick up a load and drive home that night and the local sheriff deputy is pulling me over for no lights on the trailer. Jump up and down on the trailer and they went on and off. Lucky I was close to home and the sheriff deputy followed me to my drive way. Took several days find the problem, yup, it was a bad ground.

Kansas4010 · Sep 4, 2016

I wish you would keep your trolls at your place and not run them off here. They're coming disguised as mice to fool me. They went through 3 of my trailers. I'm not sure what nutritional value they find in wires but they sure seem to like it.

Richard G. · Sep 4, 2016

John T. Bad ground is a big problem, but I have one much worse with my trailer. Letting my sons use it.
I never put my 20 foot on the road without checking the lights.
At least my sons will help me work on it.
Richard

mjbrown · Sep 4, 2016

I will add one more piece of advice from my experience with trailers at work. It is a bad practice to use the trailer frame as a ground where the lights are grounded to the frame then the frame to the plug at the front of the trailer. Use a ground wire in the harness all the way to the plug and your trailer lights will be much more reliable. I also use marine butt connectors that heat shrink with sealant on the inside. I recently purchased some aircraft connectors that have a ring of solder that melts at heat shrink temps. Haven't tried them yet.

DoubleR · Sep 4, 2016

As the others say its probably a problem with your ground. I have found that I have allot fewer problems with the trailers when I run a separate ground wire from the lights up to the trailer plug.

Leroy · Sep 4, 2016

Back as far as 03 the plug in connector for trailer is under the bed at the back end. When I had dealer put the brakes with plug on my recently purchased 03 Dakota they thought they were going to have to run wires from front to back but when started found the pulg connection so did not have to do any wire running.

da.bees · Sep 4, 2016

Considering the fact everything else is working right other than right turn,the ground is good. It sound's like someone has tied truck turn and trailer turn togeather. Vehicle and trailer circuits have been seperate for several years. I have a set of magnetic lights I bought to tow a car several years ago. I use them if I need to tow trailers that belong to other people and save time required to overhaul someone else's problems.

T in NE · Sep 5, 2016

Then they don't even wire all their trucks and trailers the same way. So now each pick-up has a pile of adapters behind the seat so that each trailer's lights will work correctly behind that pick-up.

John T · Sep 5, 2016

I know these "dudes" who always equip their trailers with pintle hitches versus the traditional 2 inch ball, I ask why, they say it cuts way down on other dudes asking to borrow it lol HOWEVER then they may want to use BOTH your truck and trailer. If I'm that way again can I borrow your trailer??? Id do it for you !!!!

John T

Richard G. · Sep 5, 2016

I have pintle hitch also. I don't trust the shanks on ball hitches. Saw too many break at Clemson.
Oldest son has 2 pintle hitch trucks and youngest son borrows my truck.
I would let you borrow mine in a minute as long as we check the lights first.
Richard

It's ALWAYS trailer wiring

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