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.