Hello,
New guy here, hoping someone can help me out. I have a 2006 CRD, purchased used last fall. It came with the 7-wire harness, with a trailer brake control. I was using a Hoppy 7-to-flat-4 adapter to test trailer lights on a small utility trailer, and after a while lost power to the running lights (on the trailer). All vehicle lights work fine, but I tested and there is no power at that running light tab any more. All vehicle fuses seem to be ok, and the trailer turn signals still work. Is there some other fuse in this system, or other likely point of failure? I have seen in other posts where the access to rear lighting plugs is in the rear passenger side. That's one big panel with no visible screws, so how do I get it off without breaking something?
A big pre-emptive "Thanks" to anyone can help!

It's a good question. Lets see if we can't get someone with real knowledge to look at this for you.

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02 Liberty Limited
Silver Outside & Taupe Inside
Heated Seats, Sunroof & Infinity speakers
USA Spec I-Pod adaptor, Mopar Sub, Garmin GPS
Tow Package, Select-Trac
Rock Rails, Tow Hooks

Is it the MOPAR trailer harness or another companies?


Some trailer pointers:
Troubleshoot Your Trailer Wiring


If you have a Modulite (powered converter), Converter, or T-One connector that is not working properly, you need to use a circuit tester to determine the source of the problem.

Check to make sure there is a signal going into and coming out of the converter or Modulite box without the trailer hooked up. The only part of the wiring harness that will typically go bad is the box, so you need to determine if a signal is making it to the box, and if so, is it coming back out on the correct wires. There are four possibilities:


There is no signal going into the box, meaning something is incorrect on the vehicle.
Solve the problem by checking for blown fuses and then check the installation points. Use a circuit tester to check that the correct wires are tapped into, the wiring harness connectors are plugged into the correct vehicle connectors, and check that connectors are plugged in all the way.
A signal is going in and coming out on the appropriate wires, then there is a problem with the trailer wiring.
Solve the problem by inspecting the wiring on the trailer to make sure all of the connections are correct and ground wires are connected properly. Most likely, the ground wire on the trailer is not secured properly. A trailer wiring system is grounded to the frame near the coupler and each light also needs to be grounded. If there is not a white ground wire coming out of a trailer light, then the light is grounded through its mounting studs. Too much paint, dirt, or rust can cause bad grounds, so make sure the ground is secured to the bare metal frame. Also look for pinched or cut wires, these are often found when wires are routed above suspension components or behind taillights
If a signal is going into the box and not coming out or a signal is going into the box and coming out on the wrong wires the ground on the vehicle may not be connected properly. If the white ground wire is not installed properly on the vehicle, then the green and yellow wires will not carry signal coming out of the box.
Solve the problem by checking to make sure the ground wire is installed properly on the vehicle. To make sure you have a suitable ground, first connect the circuit tester's ground wire to the same location as the ground wire on the wiring harness. Then test the signal going into the converter or modulite box. If there is no signal, connect the circuit tester to another grounding location such as the exhaust pipe. If a signal is present, the grounding location for the wiring harness is bad, and a new location needs to be found. On a few vehicles, the frame and body components are not grounded. In these rare instances, look for a ground wire coming out of the license plate light.
Due to extensive testing and quality control, it is very rare that a new wiring harness will be defective. If the wiring harness worked properly when installed but then went bad, there is a strong possibility that it has shorted out because of a problem with the trailer wiring. Make sure to correct any trailer wiring problems before installing a new wiring harness.
Converter Shorting Out
When too many amps are drawn through the converter box, it can be shorted out. The possible causes are:

Too many lights on the trailer. Each incandescent taillight draws about 2 amps and side marker lights typically draw about 0.5 amps each. Most converters allow up to 4 amps to pass through them. A standard converter cannot have any more than 1 taillight on each side.
To solve the problem of too many lights on the trailer, use a modulite or powered converter. It installs the same way as a standard converter except an extra wire is run to the battery so the modulite draws power directly from the vehicle battery. The modulite comes in 3 different amperage ratings. Modulite Lite for up to 4 amps, Modulite for up to 6 amps, and Modulite HD for up to 20 amps. Modulites can be added to the vehicle after a standard 4-pole has already been installed with Modulite Adapters 118193, or 118189.
Trailer connectors get wet, causing too many amps to be pulled through the converter. Water can unite all 4 wires on the trailer connector causing it to draw too many amps. This often happens when a boat trailer is backed into water with the trailer wiring still connected to the vehicle.
To solve the problem of connections getting wet, always disconnect the trailer connections before backing into the water. Also, covers can help prevent water from getting into trailer connectors when it rains or when a vehicle is taken through the car wash.
Bare wires touch each other or the trailer frame. This causes too many amps to be pulled through the converter box. The coating on trailer wires can wear thin, often at the connection to the trailer's taillight or where the wires pass over the trailer suspension. If wires are hung too loose, they can get pinched and smashed between the trailer frame and suspension u-bolts.
To solve the problem inspect the trailer wires and replace any that are damaged or frayed.
Weak Ground
If you find some, but not all, lighting functions work properly you may have a ground problem. In this situation a weak ground is just strong enough to provide some lighting functions but not all. When the taillights and brake lights are used at the same time, it creates the maximum amp load of the lights on the trailer. If a ground problem exists, it will show at this point. The places to check grounds are as follows:

The connector on the vehicle should have a ground wire secured tightly to a clean surface on the frame. A wire attached to the body or a surface with undercoating or rust can cause a ground problem
The connector on the trailer should have a wire from the connector secured tightly to a clean surface on the trailer.
Each tail lamp assembly at the back of the trailer also must be grounded. This is done in one of two ways.
The first is by a separate wire coming from the back of each tail lamp assembly being secured to the frame.
The second, and most popular, ground is achieved through the bolts of the tail lamp assembly. In this case, the lamp housing must be attached to the frame of the trailer. If the lights are mounted on wood or PVC material, the light will not receive ground.
The last possibility to explore is in the trailer design. If the trailer has a tilting bed, it is possible the ground is not passing through the pivot point resulting in a poor ground. The solution to this is to route a ground wire from the connector at the front of the trailer to each lamp assembly at the back of the trailer bypassing this pivot point.
If you purchased your wiring harness from etrailer.com and none of these fix your problem please feel free to contact us so our product experts, and installers can determine possible remedies or warranty coverage.

_________________
Brian, Blue KJ in PA
LOST#99, Mid-Atlantic LOST
Blue 2003 KJ Sport

RL Super Skinks

Thanks sleeve 84028 and Blue KJ,

The trailer wiring is new, but the trailer isn't, and it probably does have a bad ground which was causing problems. But during the process of troubleshooting this, the vehicle lighting quit working properly. (Well, not the lights on the vehicle, thankfully, but the signal at the plug by the hitch.) I have tested this with a multimeter at the plug on the back of the vehicle. Where once there was power for the running lights, now there isn't. The vehicle has the MOPAR brand 7-wire harness, and since it is listed on the original window sticker, I assume it was installed at the factory, or at least by the dealership before it was delivered to the first owner. As I said, all the lights on the vehicle work fine, and I checked all the fuses that say anything about "trailer" both under the hood and in that side panel, and they seem fine. Since one minute it was working fine and the next it wasn't, and the connection is very clean and tight, I don't think it's just something loose. Also, as I said, the turn signal power is still coming through properly, just the running light power is out. Does the MOPAR wiring system include one of these converter boxes? If so, where is it, and how do I get to it to check it out? Since the vehicle lights work fine, I figure the problem must be between where the signal splits off from the vehicle taillights and where the harness comes down to the hitch. But I don't know where that split is.

Again, thanks for any and all help!

The MOPAR harness can be seen by popping off the right side of the cargo area. See the attached pdf file for the well detailed (just kidding) MOPAR instructions...it does have the pic of what sockets feed what.

But Do NOT bother taking off the seat belt, you can open the side cover wide enough to get in without removing the entire panel. I did not remove the seat belt when I put mine in 3 yrs ago and had plenty of room.

http://site.justforjeeps.com/guide/82207248.pdf

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Brian, Blue KJ in PA
LOST#99, Mid-Atlantic LOST
Blue 2003 KJ Sport

RL Super Skinks

That's perfect, just what I need, I think. You're right, some descriptions would have been nice, but you take what you can get. I'll try this as soon as I get a chance. Hopefully this weekend. Thanks again, Blue KJ!

Ever figure out this problem?

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Brian, Blue KJ in PA
LOST#99, Mid-Atlantic LOST
Blue 2003 KJ Sport

RL Super Skinks

Just wondering but what are the additions 3 wires for in the additional harnes for battery power? I just went from the European 7 pin harnes to the 7 pin US harness, both MOPAR.

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No longer a CRD or Jeep owner. Selling everything I have, needs to go as I need the room for a project.