I have a straight 4-prong trailer connector on my truck and each time I've used a trailer the lights have never worked properly. I have an old Jayco tent trailer that I hooked up using a Jayco factory adaptor. Orginally, the trailer lihgts didn't work right and I spent hours playing with the harness on the truck before I was able to get it work right. Turned out that one of the wires on the 4-prong had to spliced into one of the wires for the tail light.

Well, this year I bought a utility trailer and had issues from the beginning. My dad and I stripped out and re-wired the whole trailer. We had everything working fine but I decided to check the lights about a week later and sure enough, the running lights weren't working on the trailer. Before re-wiring the trailer, we were blowing fuses left and right trying to diagnose the problem.
So, while I was visiting my dad recently he decided to have another look at it. He simply disconnected the rear harness from the main harness and reconnected it and we lost the running lights on the truck! Turns out we blew another fuse! We got the running lights working on the truck but we still can't get them running on the trailer. My dad and my brother also own Fords and they have the same type of issues.
Has anyone else run into a similar problem? If so, how did you rectify it? I'm tempted to go to an RV place but I'm also concerned that if they get my lights working on the utility trailer then my popup camper won't work!

 

Hey,
I'm having the same problem! I 'accidentaly' put a nick a wire on my trailer while adding some atv tie downs and shorted out my marker lights. I didn't realize it until I was testing my lights to head out. After fixing the short on the trailer (all is fine with the trailer lights now) the maker light pin on my 4 prong connector does not have any power on it. All the fuses seem fine, and the truck lights all work. I think I must have blown a fusable link, ANYONE HAVE ANY IDEA WHERE TO FIND IT????

Your problem might be along the same lines. Check the connector on your truck for power (1 pin for left turn/brake, 1 pin for right/brake, 1 for marker lights, 1 for ground). Walmart sells a cheap tester for them (about $5) which makes life easier.

Good luck!
Radar13

 

The first order is to wire your connector to the "Standard" wire code per function.
That means pin x is the tail/marker lites, pin y is the left turn/stop etc.
Then when you connect any trailer to the truck that should also normally have the same standard, you should have no compatibiliy problems unless there are faults present or the trailer is 'butcher' wired.

For a free reference, go the an RV dealer and get a copy of the TEKONSHA catalog, free and look in section on tech for the standards for the type of connector you have.
Until you get a handle on this, the problems will be ongoing.
All you need to do for testing operation is use your 4 way flashers to test the left and right turns and the parkers for marker lamps all in one shot.
I do this almost once a week when hooking up to go to the race track.
Then you know the wiring on the trailer is correct once it is done the first time and see a problem after that, is a fault.

 

Having worked in the area of installing hitches and harness's, I can tell you that first of, the four way idea will only tell you that your four ways are working. If you have accidentally crossed the left and right turn signal wires you won't know this by checking it that way.

Second, the running lights on the trailer should be running on the same wire as your tail lights and your turn signals are on two separate wires. If you have a cut in the wire then it may be touching metal and that would be the cause of your blown fuses, as you have a short. You should first make sure that you have either taped that wire casing shut or have, better yet, replaced it. If you are still experiencing this problem then you may have to use a stronger fuse.

This is only true on a four prong harness. One for running lights, two for turn signals (one for left, and one for right), and then your ground. Your brake lights will run automatically through your turn signal lights, and shouldn't be a problem.

Also make sure that you have installed a heavy duty blinker after attaching the wire harness as you are now running the turn signals on your trailer as well. If you don't then you can expect to have to replace your blinker again soon. This is found on your fuse box, it will be the big cylindrical fuse. This is what leads me to believe that you may very well have to go to a stronger fuse.

Post if this doesn't work and I'll check into further issues.

T

 

ureagletz, you missed a small point.
Once the system has been wired correctly and checked including the trailer, the 4 way test is fine. It has to work anyway to be legal.
This should tell him that both sides have no shorts or opens right up through the truck's harness, then a check of left and right should be done before going on the road.
I followed an open lawn equipment trailer today that I almost didn't see the turn signal because there was a wire error in that system that allows the tail lamp to stay lighted apparently with the brakes while the other filiment in the same bulb flashed. Not good in the daytime. Who ever did the wireing and checkout was out to lunch!

 

Not the point though here bro. First, as they have it stated above they have pulled the wiring harness apart and have rewired the trailer, possibly on a number of occasions. But, they aren't looking for directional issues here. They are looking for the reason that their trailer harness is shorting, or blowing a fuse over and over.

Besides, just because your four ways are working doesn't neccessarily mean that your turn signals are working. If you'll notice, I have a thread started where I am requesting a wiring schematic. The biggest part of my problem is that my neither my running lights or turn signals are working. However, my four ways are working perfectly. So I obviously have a problem in my turn signal somewhere. So definately do not continue to rely on that method of inspection.

My best guess is that they have a bad ground, a cut (exposed) wire, or have to upgrade their fuse.