Let me start off by saying that I don't think the problems are with the truck- the trailer it's hooked to has given me problems in the past.
Here's what I'm up against- trying to get ready to pull our 28' camp trailer 600+ miles starting tomorrow afternoon. When I pulled this trailer home last fall about 5 guys spent about 6 hours trying to figure out what was going on with the wiring. We got it close enough and jerked the thing home.
Now tonight I hook ye olde gold money pit up to the trailer. Turn on the headlights- only one tail light and no clearance lights... hmmm not the end of the world I guess. Hit the right turn signal and left lamp comes on along with clearance lights hit the left turn and only the left lamp comes on Hit the brakes and all tails come on, along with all clearance lights Unhook the trailer and take a test light to the plug on my truck- the only thing I get is +12V (in the right spot too). Luckily I think we will be able to avoid driving in the dark, but should I check relays/fuses on the truck or just say to halibut and roll out.
I'm very tempted to rip all the wiring out of this damn camp trailer and re-do it from end to end to make sure everything is right AND I have good ground (that was the biggest problem last time).

 

Chase, there are few things as frustrating to chase down and fix as faulty trailer wiring. My experience has been to rip out the old wiring and start over that way you know what color wires are going where. With the different trailers that I pull on a consistent basis I have had pull all the wiring out and start over. It seems that you can never fix the wiring it all has to be replaced. I feel your pain and hope you find a simple fix. Just a thought, some manufacturers wire the 7-way plugs differently. I have run into this before on two of our trailers so you might double-check the plugs and verify that they are wired the same as the plug on the truck.

 

The trouble is, how do I verify the wiring on the truck if I'm only getting +12V at the plug? There is nothing, and I mean nothing, I hate worse than vehicle wiring problems.

 

you have ground problems for the most of it

 

Do you have a multi-meter and not just a test light? Sometimes you will be getting a lower voltage value which can really screw things up in the trailer wiring. Just off the top of my head are some of the wire colors:
blue-brakes
green-signal/brakes
yellow-signal/brakes
brown-running lights
white-ground
red-reverse lights or aux
black-battery charge for breakaway or aux
If you have the factory plug on your truck there should be a little schematic of the plug on the weather cover.

 

Chances are you have a bad ground, and 1 or 2 crossed wires.

Honestly it will be easier to re-do the wiring. I've been in this boat a few times, and it's usually a head banging fight for hours leaving a fixed but old and weathered wiring system.

First, get a test light and verify the truck is putting out good voltages.

When re-doing the wiring, Solder connections and use heat shrink tubing. Place new wiring inside old garden hose to keep it protected. Dont use any of those "quick connect" connectors, they corrode and eventually fail.

Can't stress enough: SOLDIER CONNECTIONS, HEAT SHRINK TUBING ON SOLDIER JOINTS, AND PLACE WIRING INSIDE OLD GARDEN HOSE.

 

the best way to check your plug on your truck is turn it on, turn headlights on turn on your four ways, and have some one hit the brakes,take your test light and find which prong does which , then pull back the cover on your trailer plug and match up the prongs that u just tested, and use the colour code that mike suggested to find out if its all alright.

green-signal/brakes
red -signal/brakes
brown-running lights
white-ground
yellow-reverse lights or aux
black-battery charge for breakaway or au

 

first thing check ground, move tr and trailer to asour ground,or run wire from toung to hitch , clean all connections, bad ground just was my problem to new trailer , 02 tr
good look can be real head banger

 

I will agree with what was already said, to start over and rewire the whole thing. I am assuming you are talking about the 7 way RV plug on your truck. Here is a link that might help you trouble shoot your truck and trailer wiring, it has diagrams and pics of the plugs. Also I had a problem with my brand new toy hauler with my truck. It was blowing fuses for the running lights in the truck when I would go into or past reverse, my hauler has no reverse lights so I just pulled the relay. After that I was blowing fuses in the hauler when I turned on the rear lights until I removed the female contact in the middle of the truck plug Just a sugestion to look @. Good luck and safe travels.

 

Ground problems are exactly where I would start, remove every fixture, clean the bulbs,clean the point where the screws touch the fixture, resecure the fixture to the trailer. You back feed one of the lights, and you get all sorts of "blinking", from brake lights, turn signals, ect. I would grab a beer, a ladder, and cordless.. just take your time, oh yeah, sand paper.

 

Ground. Ground. Ground. The ball is a bad ground source. The problem is most likely rust in the trailer coupler. Did I mention a bad ground?

 

The symptoms sound a little worse than a grounding issue, although you'd be suprised what a couple bad grounds can do...

If the wiring is more than a few years old, I'd redo it, and redo it right. Like i said soldier connections and heat shrink tubing, and run old garden hose over all the wiring.

I may be approaching "broken record" status on this one, but I'm just trying so make your life easier in the long run....

 

een wire nuts work better than crimp conectors

 

I'll agree that new wiring is probably the best for the long run. But even new wiring won't be worth squat with a BAD GROUND. If the ground was the problem before, i'm bettin that it still is. Besides....it is the quickest thing to troubleshoot and correct. Run a new ground from the truck chassis to the trailer chassis. Jumper cables would work for a diagnostic tool.
I have 5 trailers here. The wiring is good on all of them. If I latch onto one I haven't pulled in a while, it might be a few miles and a few more hard turns til the rust is cleaned off enough to let the lights work.
You may be lucky enough to pull in the daylight, you will still need the brake lights.
Have a great weekend.

 

That is what was done last fall when we were getting ready to drag the trailer down here, don't have time to go through it all again before leaving today.

I already checked the connector on the truck with my test light- read my first post.

The plug on my truck is not factory, but when I hooked it up each screw was labeled with what color wire was supposed to be under it. The weirdest thing to me was that with the trailer unhooked the only thing I got at the plug was +12V but with the trailer plugged in random lights were coming on. I'll try and mess with it before I leave today- wish me luck.