Faulty Trailer Lights
 

My 2500 Mega-cab has two trailer plugs. One seven pin circular and a staight four pin.
About a month ago after blowing the trailer fuse, I started having this problem. I have running lights only on any trailer I tow. No brake lights and no signals or emergency flashers.
The fuse was replaced under the hood.

I have tried to research this problem and did come across a similar problem someone was having and there ended up being a second fuse box in the cab of his Ford. I have checked every fuse under the hood and can not find a bad one. I also tried following the trailer plug wiring as far back as I could and did not find a hot wire to the signals.

This seems to be a fuse/signal stat issue but I can not find the source. I will be towing a 10,000 lb. trailer from CT to New Hampsire this week-end and I don't like the idea of running without signals or brake lights.
I sure could use some help.

Have you checked the trailer plug on the rear of your truck? :

This will help a lot: How to Wire your Car or Truck for Trailer Lights

If you use a tester and start at the plug on the back of the truck, just pick a wire and test it every few feet as it makes it's way to the front of the truck. This will show you where the problem starts at. It may be whre the trailer wiring actually connects to the lighting system but if it's factory wiring that now a common thing.

If it's factory it could still be covered under warranty if so let the dealer fight with it. As a quick fix here to get you on the road you could also just pick up one of the Hoppy brand quick plugs that hooks right into the lighting harness under the rear bumper and run a new plug.

This guy can help you for sure...

I did start at the plugs.
There is power to the plugs, both circular and straight plugs have power going to the running lights, neither have power going to the signal lights. I traced the wires as far back as I could reach. I believe one is green and the other yellow.
I removed the fuse block from it's holder and tried to trace the trailer fuse location on the block to the actual wire harness, couldn't pin piont the wire group coming out of the fuse block.
I have power to the running lights, just no signals or brake lights.

I'm makin some assumptions here so bear with me. All the lights on the truck themselves work including brake and turn signals right.

This is a factory wiring set up and not an aftermarket.

Going in a clockwise direction stating to the at the first pin after the alignment nub on the 7 pin they should be the following colors and in the same order as listed. Kinda confusing I know.

Blue/Electric Brake
Green/Right Turn Signal
Any color/Auxillary. Spare plug for larger trailers, back up lights or anything else you want.
Brown/Tail lights and Side Markers
Yellow/Left Turn Signal
White/Ground
Black wire should go to the center pin.

Now if you use the tester use a nail or straight pin to probe the ground pin hole and use it to test the other pins. This will also tell you if it is a ground problem. If you have a faulty ground and not just completely bad sometimes it will cause just some lights to work. By testing like this the ground will either work for all of the lights or none of them. Check power to all the pins. If you still come up with no power to the same lights I would reccommend taking a spare fuse or trading fuses in the lighting slots to see if that fixes your problem. I have also seen several fuses that were bad but didn't look burned through when you just looked at them.

After typing all of this it dawned on me that it would be easier to go through it using the 4 pin flat connector.

White/Ground to trailer, it's the only bare pin.
Brown/Tail lite, Side Marker
Yellow/Left stop and turn signal
Green/Right stop and turn signal

Let me know what happens after you swap fuses. I'm bettin that this fixes your problem if my assumptions are right.

Be sure you try to swap both the trailer relay and the fuse.

If all else fails this will get you back up and runnin in the quickest and cheapest fashion.

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"I'm makin some assumptions here so bear with me. All the lights on the truck themselves work including brake and turn signals right.

This is a factory wiring set up and not an aftermarket.

Going in a clockwise direction stating to the at the first pin after the alignment nub on the 7 pin they should be the following colors and in the same order as listed. Kinda confusing I know.

Blue/Electric Brake
Green/Right Turn Signal
Any color/Auxillary. Spare plug for larger trailers, back up lights or anything else you want.
Brown/Tail lights and Side Markers
Yellow/Left Turn Signal
White/Ground
Black wire should go to the center pin.

Now if you use the tester use a nail or straight pin to probe the ground pin hole and use it to test the other pins. This will also tell you if it is a ground problem. If you have a faulty ground and not just completely bad sometimes it will cause just some lights to work. By testing like this the ground will either work for all of the lights or none of them. Check power to all the pins. If you still come up with no power to the same lights I would reccommend taking a spare fuse or trading fuses in the lighting slots to see if that fixes your problem. I have also seen several fuses that were bad but didn't look burned through when you just looked at them.

After typing all of this it dawned on me that it would be easier to go through it using the 4 pin flat connector.

White/Ground to trailer, it's the only bare pin.
Brown/Tail lite, Side Marker
Yellow/Left stop and turn signal
Green/Right stop and turn signal

Let me know what happens after you swap fuses. I'm bettin that this fixes your problem if my assumptions are right.

Be sure you try to swap both the trailer relay and the fuse."

uncle bubba,
all your assumptions are correct.
The fuse is good, and I also tried two others.......now, please pardon this next question.
You mention a "trailer relay" this is the item I suspect but I do not know it's location. I looked for a reference in the owners manual and found none. It is not identified on the fuse block either. Would you know it's location?
Let me also thank you for your efforts here, you are good people.

I'v never dealt with a Dodge as new as your but on the older models it's in the fuse block under the hood. There is a row of 4 relay's and the trailer relay is the first one closest to the drivers side.

If it were my truck there are things I'd do to test it but I don't want to suggest them for somebody elses truck cause the newer the truck the more sensetive the electronis on them and I'd feel like a real heal if I suggested somethin and it didn't work out right. So naything you do in that under hood fuse box, please think closely about and use your own discretion. I've been in the trailer business for years and refuse to go in there with customer trucks because of liablity reasons.

Personally I'd pull that relay and fuse and turn on the lights just to see if I had power to that point. Since you have power to the other trailer lights the relay should be good. So your problem will be in the factory harness connector and I'd check with the dealer about a warranty on that one.

Doin some lookin through parts books here and it looks like the factory harness for your truck plugs right in under the rear end, should be nothin comin from the front of the truck to control just the trailer. A replacement factory harness is only about 3 feet long. It's all fed from the truck wiring to the rear. So if you have no power to the back of the truck you have a problem in the truck lights. In the end this tells me that you probably have a grounding problem and just need to clean all the grounds off and smear some di-electric grease on them. I also keep the terminals filled up with this grease to keep them from corroding myself. Wish I could offer more help here.:argh:

The problem is.....I can not locate a relay. The fuse block has all fuses-10amps to one 40amp. This is my next quest.
Uncle bubba, I would never hold anything against someone willing to take their time to help me when asked.
Thank you

From what I have found it doesn't look like your gonna have a relay. It's all controlled by the main switch to the rear of the truck.

Uncle bubba,
I will start at the end of the trailer harness, clean it all up and grease it all up as you recommend....'

"Wish I could offer more help here.''

I owe you much, thanks again!

Did you get your trailer lights fixed?

No, the promlem is in the fuse box. The trailer fuse blew about a month ago. That fuse was replaced and the lights never functioned correctly after that. The wiring from the trailer plug all the way up to the fuse box is in tact and grounded.
I took the apart the fuse box and I believe the computer board inside was damaged when the fuse blew. I thought the fuse would have prevented this from happening. I will take the truck to the dealer this week.

Many thanks to you and uncle bubba for the help, it is much appreciated.

have you tried pluging the trailer into another truck to see if it's the problem?

He said he didn't have power even to the trailer hook up. I'm hopin he comes back and gives us a status report. I'm still curious to know what it turns out to be.

dumb question again but did you test the plugs with the brake pedal pressed? if the brake pedal isn't pressed then there will be no power to the plug. if there is no power there after the pedal is pressed then i'd look into the brake switch under the dash that turns the brake lights on. have you changed the fuse that you replaced with another good one? i've seen some fuses look good and be bad before.

just thinking outside of the box here and my post is not to make anyone feel stupid cause i've made mistakes too when checking stuff...... just going back to the basics....

I had him change out the fuses and relay's along with switch em around with known good ones. But I missed the part about askin if the brake pedal was depressed when he checked the power. Damn, and I thought I was bein so carefull about tryin to check for the obvious first. Guess that's the hazards of doin this stuff over the net.

Closing this as he was due to use the truck this weekend. Im assuming this is fixed - if not, you are free to reopen it.

Faulty trailer wires-revisited
 

This is a follow up to the now closed out post.
I brought the truck to a Dodge dealer close by.
They said there was a tech bullitin sent out that had to do with a software down load. When I got home I checked all the wires and I did get power to all lights.
The only problem is, I have an in cab electric brake unit that now has constant power even with the key out of the ignition. This was never the case before. When I called the dealer back up they said this was normal and that is the way it is on his personal truck.
How could this be "normal" if it wasn't this way BEFORE they did the software down load.
I don't feel very good about this dealership. I asked them for a copy of the tech bullitin and they said they would send me a copy. They also charged me a half hour labor, I asked what for and they said it isn't covered.
Does any of this sound a little sketchy to any of you out there?

In factory plug mode you will have power to the brake all the time. In most controllers you will only have a little red light stay on though and not the number and control panels. They draw most of nothin for amperage so it's not gonna affect anything. When you wire them yourself you can draw power from any wire you want to control when it comes on but there's no switch on your trailer lights to turn the plug on and off. When you plug your trailer in they are hot all the time.

Glad to hear it all got worked out though. By the way, I have done very little dealing through the dealers so I'm no expert but it was always my impression that tech bulletin items were fixed free of charge. Like I said I may be way off base there.:c:

Tech bulletins are not usually a "freebie" , unless it is covered by warranty , and then it's usually called an " update". Recalls are always free , be it under warranty or not.

The original poster can always reopen their support threads if the issue pops up again.

I went ahead and merged the two threads for you in case you need to reference the whole thing again.

I agree with Uncle Bubba on the box having power all the time.

Are we Done Here?

Yes sir

You managed to get it fixed??