I have a 1999 Ram 1500 Sport 4x4 with the basic 4-flat factory towing package. Very soon I'll be pulling a car hauler and a horse trailer quite a distance and I need trailer brakes and what not. I know I'll have to be pulling bigger trailers more frequently so I want to put in a decent brake controller. I plan on using the Tekonsha P3, since it covers just about every use I could ever hope to need. I know my truck has the factory "electric brake" harness and connector under the dash on the driver's side, and I can just plug the controller into that, but I'm not sure what to do about the actual connector at the rear of the truck. I have the 4flat connector back there, but I don't see any extra wires that would be for the brakes and reverse lights and what not.

I wonder where do the wires that the brake controller connects to in the cab go if they are not present in the rear? Maybe I'm just blind and can't find them, but I'm almost certain they aren't there. So what do I have to do to install a connector identical to the factory 7 blade connector present on 2500/3500s, ideally without having to run wires to the battery (because I was pretty sure that the 3500 trailer connectors are all self contained, being that they are factory installed). I want to keep things as close to stock and without adding bunches of extra wires.

I'm not sure if what I want is possible, but I am willing to spend my money and give myself a headache keep myself sane down the road. All help is appreciated lads

 

On my '96 Ram 2500 with the factory trailer package option, just behind the rear bumper up on the left side of the frame, there is a factory wiring harness for the trailer wires. My truck came with a trailer hitch and 7 pin connector attached to the trailer hitch surrounded by a rectangular metal protection area. Check your frame area there to see if you see the trailer wiring harness on your truck.

 

this is the only wiring I've got back on the left side behind the bumper. I'm guessing that I actually don't have the factory tow package, because I have a hidden hitch receiver and some terrible splices. This one big group of wires comes back, splits off into the right taillight​​​​​, then gets spliced off to the trailer hitch, then goes to the left taillight.

I do have the blue 4 pin connector underneath my dashboard that says electric brakes, but i have no idea where those wires go. It doesn't look like they are present at the rear of my truck.

 

To me if looks like you have the wiring as that purple? Wire is really thick which would have went to the 7 pin connector

 

what is the purple wire? i have a wire that looks purple in some spots but it's also blue. the whole wire seemingly fades from purple to blue in sections.
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I have the factory brake controller plug under the dash, so I wonder where the wires go? If they're all present, they have to be somewhere and i would prefer to use them over splicing and running all new cable.

I also have a white wire with a brown stripe that ends and is capped, I have no idea what it is.

 

The trailer wiring for your truck should be located within that harness on the left rear side of your truck you showed in the photo. If you are going to use the Tekonsha P3 brake controller in a plug and play manner, you will also need to purchase the wiring harness that connects the brake controller to your factory underdash plug if you don't already have it (https://www.etrailer.com/Accessories...ha/3020-P.html)

 

I don't think there was a factory tow package that only had the 4 wire connector so likely you're right and the hitch was put on later. My truck didn't have the tow package either but the first owners (state government) added the hitch with 4 pin, 7 pin RV and 7 pin agricultural to it. Tapped into the harness at the rear just like your pic. Still it didn't have the brake and permanent 12V to the rear. The brake wiring is present in the cab and ends at a connector under the left rear of the cab. I added two wires for brake and 12V from there to the rear.

 

IF you have the blue (brake) wire running from the front(plug in the cab) to the rear it had to have the 7 pin plug at one time. I don't think you could get the tow package with the 4 pin. They didn't have a need for the brake controller. I would check continuity of the blue wire in the cab to any blue wires at the back.

 

I have the blue connector under the dash, with what looks like a red wire with an orange stripe, a white wire, a blue wire, and a black wire. The wires go out the firewall and it looks like I found them with the dual connectors where the front left tire is, right next to the suspension components. Two little electrical connectors are mounted to the body. It looks like all the wires come out of one big piece of conduit, they split off into the two connectors at about 6 or 7 wires a piece, then after the connectors they all rejoin each other and run to the back of the truck. I think I managed to find the blue wire here, in this mess of wires, but I'm not entirely sure because this is an off-road and working truck, the wires are almost all black with mud. But from the spit and my fingers, I seemed to find the blue wire and the red with orange striped wire. I believe there is already a white wire in the back, but if that's a ground I can create me own.

It's strange to me how all the wiring is seemingly present in the front, and makes it all the way down to the conduit that runs to the back, yet somehow seems to vanish right after it goes into the conduit. Maybe some day soon here I'll take apart the conduit and see what the wires do when they get recombined before they run to the rear.

 

Sorry I wrote rear of the cab but it's near the front body mount. If you look closely at the connector you'll find one side has less wires than the other. If the truck didn't have the tow package the trailer brake wiring ends there.