The trailer light thing

I often see trailer lights discussed and they can be a pain. I have a wire attached to my trailer frame, with plug and one on my truck
frame with the opposite plug end . This is in addition to the 6 prong plug with the ground wires incorporated in it . Many believe that the
trailer will ground itself back through the hitch but that's a myth. So I have a direct ground along with the wired ground wires and I
never have a problem with trailer lights. I used to maintain a fleet of 20 trailers for a mechanical contractor and I can guarantee you
that 90% of all light failure is due to a bad ground. I even ground the tail lights to the trailer frame with a short piece of wire , and
self taping metal screws
I also did electric trailer brakes, cause for failure there was a wider scope. Usually the magnets were burned and not functioning . The
actuator arm was rusted and siezed and wouldn't appy the brake shoe . The adjusters were siezed and the shoes not making contact with the
drum. In terms of time and money the boss and I discussed rebuilding brakes vs buying the complete assembly. A new brake assembly goes on
with four bolts and splice of two wires and done. The labour savings are signifigant. I will say one thing about electric brakes , they
can be working fine one day and the next day they aren't ! You can check by having someone put the brake on in the truck and you should
hear them humming..SO...Ground ! Ground ! Ground ! and your lights will be good to go !

Forgot to mention that my trailer wiring is enclosed in conduit with junction boxes all attached to the frame so I never have damage to the wiring from being snagged or frayed . It took a bit of time but all worth it. I haven't had to do work on my trailer lights in years

Not as big a problem now that many trucks come from the factory with trailer wiring but years ago it was often seen where someone would wire up their own vehicle and trailer without following standards for what pin does what.

Works fine until somebody borrows or sells the truck or trailer and tries to hook it to something wired to standards.

Then the fun begins.

I was talking to a guy just last week he was towing a trailer home just as daylight was fading, as soon as the automatic headlight sensor turned on the headlights and tail lights his brakes on the trailer locked up.

Pretty easy to guess which wires were crossed on that one.

I agree with you. I also shine up the metal where the ground wire goes and grease it to give it long lasting connection. Had a guy at work that said the brakes on the trailer work when you manually put the trailer brakes on. He said he could feel the nudge when he applied them. But he still almost slid through an intersection with it. Long story short, on a 3 axcel trailer only one brake worked. The other 5 brakes were either seized up or the wires were broken. Only one brake was giving him that nudge feeling. I do believe like you said, brakes can work one day and not the other.

AMEN I was a used truck tractor and trailer dealer plus farmed and am an electrical engineer and agree 100% ITS GROUND GROUND GROUND so often the problem......I have ran a dedicated ground wire FROM BATTERY - POST all the way back to the trailer ground wire plus hard wired it to the trailers frame along with brake and light fixture additional grounds NOW THATS A GROUND !!!! I found if you do that and any of the connections/splices I crimped, then soldered, then heat shrank, then covered with liquid tape youre good to go yayyyyyyyy

John T

I've found the best way to wire is to run ground wires to everything and not ground to the frame. I use electrical cords for everything, the wire is better quality and the double coating eliminates the need for conduit, which is prone to holding moisture. I run a two wire cord down for the brakes and a three wire down each side for lights. An additional two wire for side and front clearance lights. I mount all lights in boxes and make sure all boxes have bottom drain holes and top vent holes so they stay dry. I even put drain and vent holes in the plastic junction boxes as they sweat and stay wet and go bad quickly without them.

As jon f mn says I bypass the trailer frame completely and run ground from truck directly to each light.

Eliminating the need to ground each light and the plug ground to the frame. Doing that is just more work for little gain.

Never have trouble with lights, its the darn brakes. Burnt magnets, shorted magnets, wire shorted to the clip on the arm, wired shorted in the axle cross over. Absolutely infuriating as they are wired in parallel on most trailers. With the salt here any use of wire probes ruins 6-12 of the wire near the probe site. Next redo I'm contemplating a junction box with each brake wired individually so it can be taken out of circuit and tested alone.

Yep i get a little OCD over trailer wiring I go overboard on the ground thing as i go to the main ground back to the Battery all lights and brakes are tied into the main system ground then back to the truck , i ues a semi 7 way plug this also messes with the Can i borrow your trailer and i also wire to semi not R V here again this stops the can i borrow crowd . At the truck it goes into a sealed junction box with breakers and i use a 6 12 gauge with one 10 Ga. ground For the truck and trailer . That runs up to under the hood to another junction box where all the feeds come off relays that are breaker protected with a main power feed from the battery to the relays . This takes the strain off the wimpy truck wiring and switches they only act as a trigger for the relays , also the trailer is a dual lighting system as SOME of the markers and with dual tail lights are on one system and Some of the markers are on the tail light system so IF one system has a failure ya still have SOME tail and markers working , this also allows for a marker Bling switch to be installed for the OLD SCHOOL drivers that still blink markers when passing .

We have more than our share of problems up north, because of corrosion from road salt! All the trailers I have ever built tilt, so I have to run a ground around the hinge point, it will work for a few years without, but sooner or later it doesn't. I just had to do some work on a coupe of trailers, new waterproof lights on a boat trailer, and replaced a sealed unit. I really like the sealed units that pop in a rubber grommet, they're expensive, but reliable.

I want as few wires as possible so I use trailer frame to ground each light. I braze a brass machine screw pluse a short piece of copper strap or pipe near each light and brake plate. I take one wrap around screw and leave a tail on wire to be soldered to copper piece. Brass nuts clamp wire on screw. If on the road or emergency light replacement will have ground clamped to screw and the tail is soldered later in shop. Some wiring is in emt and some in flexiable conduit because I often run through brush and weeds.
I wonder if they will soon make insulation on wire sold over the counter from material like manufactures use which attact's chewing animals.

Helps to use good wire too. Marine grade if you can find it. Ever since I started using the marine grade wire instead of the auto parts store garbage, the only problems I've had with trailer lights are from backing into things.

Yup, bad grounds were about 90% of the problems I say inspecting trailers.

And if all else fails, carry a few extra pairs of vise grips for clamping down ground wires. Plus some duct tape around the handles so they don't come unclamped while driving down the interstate.