Mopar 7 pin trailer wiring harness - no tail lights

[KJ604]

installed my mopar 7 pin wiring harness last year long before i ever had a trailer and now im seeing i dont have running lights. both signals and brakes work but I have no constant lights with the parking lights turned on in the jeep. has anyone seen this before or did i do something wrong or did i just get a bad harness?

 

[sota]

which harness did you get

 

[KJ604]

I got the Mopar harness that just clicks in to the two connectors and then there is the wires for the brake controller that I don't use so they're j aust bundled up and stuffed behind the panel in the trunk.

 

[sota]

does it have a box?

 

[KJ604]

No box

I got Mopar PN 82207248AB

 

[Billwill]

I am busy working on a trailer hitch light problem on a different vehicle and Googling the pin layouts I see that the USA 7 pin round connector has a different layout to the British
12N British Standard that is used on our vehicles here in South Africa....including my Export 2.5 2002 RHD CRD.

I assume your Canadian has the USA Standard pin layout but a lot of the Canadian KJs seem to have some "Export" characteristics as apposed to the USA models.

So I would advise that you Google for the correct trailer harness pinouts for your KJ...make sure you are looking at the correct connector because obviously the "trailer" connector is a mirror image of the "vehicle" connector.

 

[turblediesel]

Somewhere along the way I picked up a tester for the 4 wire trailer plug with LEDs that show what's blinking and lighting up. Then I got a 7 pin trailer wire connector with LEDs that does the same. It's meant to be installed on the trailer wiring but works fine as a tester. Both have been a huge help for troubleshooting and deciding whether the trouble is in the tow vehicle or the trailer.

Vague memories of the service manual have me thinking there's a few relays behind the mesh stash on the right side of the luggage area that are part of the factory tow package. Maybe you need them as well as the mopar wiring harness you already got to make it all work?

 

[TwoBobsKJ]

No box

I got Mopar PN 82207248AB

If your KJ did NOT come with an EVIC from the factory you have to purchase the "supplemental harness" to complete the install.

I never did figure out why the additional harness is necessary but my KJ didn't come with an overhead EVIC from the factory nor with a hitch or trailer harness. I bought both harnesses and installed them per the instructions and all lights work.

The supplemental harness has additional power wires that plug into the power outlet next to the cubby in front of the shifter as well as the extra wire for the brake controller. Like I said, I never figured out how the KJ harness with the EVIC differed from a non-EVIC KJ but my guess is the the supplemental harness added power to the 7-pin - including the running lights.

The price is cheaper than when I bought mine a few years ago - I found this on the web:

Supplemental Harness - Trailer Package


Bob

 

[KJ604]

If your KJ did NOT come with an EVIC from the factory you have to purchase the "supplemental harness" to complete the install.

I never did figure out why the additional harness is necessary but my KJ didn't come with an overhead EVIC from the factory nor with a hitch or trailer harness. I bought both harnesses and installed them per the instructions and all lights work.

The supplemental harness has additional power wires that plug into the power outlet next to the cubby in front of the shifter as well as the extra wire for the brake controller. Like I said, I never figured out how the KJ harness with the EVIC differed from a non-EVIC KJ but my guess is the the supplemental harness added power to the 7-pin - including the running lights.

The price is cheaper than when I bought mine a few years ago - I found this on the web:

Supplemental Harness - Trailer Package


Bob

I thought that was only if you want to run brake controls. I thought even without the supplemental harness a 4-pin connector would still work properly.

Is that the harness you have to run all the way up to the front of the truck somehow? How bad is the install?

 

[TwoBobsKJ]

I thought that was only if you want to run brake controls. I thought even without the supplemental harness a 4-pin connector would still work properly.

Is that the harness you have to run all the way up to the front of the truck somehow? How bad is the install?

It is weird - that's what I thought but since I wanted to have brake controller capability I just installed both.

Yes, the supplemental harness has to be run from the right rear panel in the cargo area to behind the dash and then one wire through the firewall to the battery. It's actually not difficult at all - the harness is built exactly to length. Hardest part is just popping off the internal trim pieces along the bottom of the doors. I didn't completely pull the right-rear panel as the instructions said - I was able to get the harness under/behind that panel and run it under the trim of the right-rear door then around to behind the dash. Being able to remove the glove box in our KJ's makes the task very easy in the front.

Bob

 

[KJ604]

Ok thanks Bob. I guess ill have to try that.

Has anyone else installed only the one harness and gotten a 4 pin connector to work?

 

[turblediesel]

My '05 CRD Sport came with the tow package but no EVIC. Came with the 7 pin socket and an adapter to 4 pin. I added a trailer brake controller but I didn't know there was a harness available so I wired it to the power distribution box under the hood. Trailer brake wire from the 7 pin socket was behind the panel on the left side of the driver's footwell.

Don't know if that helps; Sounds like you're adding all of it.

 

[KJ604]

I added the supplemental harness as bob suggested and I now have working running lights on my trailers. Ended up only costing me $40 CDN because i found someone on ebay selling them for $6. Cost $30 to get it shipped to me but still better than the $75 the Canadian site wanted for the harness.

The install was not too bad just tedious feeding the wire through the panels to the front. Except for the get through the firewall part, that was annoying. I was trying to figure out how to nicely get the wire through it but there is just no good way to see the plug in the firewall from the engine bay. I ended up just pushing a coat hanger through blindly from the inside and then taping the wire on and pulling it back through.

Anyways glad to have proper lights on my trailer now. Thanks again Bob!

 

[Adam Roby]

Wish I had noticed this thread before. For the 4-pin wiring you don't need to run anything to the front and you don't need any harnesses. There are only 4 wires to connect + ground. Left flasher / right flasher / brakes / and running lights all done in the rear taking off the back lights with 2 screws on each. You need a light converter because trailers have a single lamp for brake and flasher whereas the Jeep using two different bulbs. The converter basically does an exclusive OR on the two and combines them to one.

I don't really get why you'd need any extra harnesses for the brake controller. If you are already running power from the battery to the brake controller, then the brake controller to the hitch... why not just run the brake signal back from the hitch to the controller using the same route? Avoids any harnesses... just another wire.

 

[uss2defiant]

the brake light and signal light aftermarket isolators are typically just two diodes.

 

[KJ604]

Wish I had noticed this thread before. For the 4-pin wiring you don't need to run anything to the front and you don't need any harnesses. There are only 4 wires to connect + ground. Left flasher / right flasher / brakes / and running lights all done in the rear taking off the back lights with 2 screws on each. You need a light converter because trailers have a single lamp for brake and flasher whereas the Jeep using two different bulbs. The converter basically does an exclusive OR on the two and combines them to one.

I don't really get why you'd need any extra harnesses for the brake controller. If you are already running power from the battery to the brake controller, then the brake controller to the hitch... why not just run the brake signal back from the hitch to the controller using the same route? Avoids any harnesses... just another wire.

The problem was because I wanted a 7 pin plug to have the ability to do 7 pin or 4 pin. If you know you only want 4 pin there is a simple harness that plugs into the existing tail light harness and runs a 4 pin plug.

For the 7 pin harness from mopar, it plugs into the tail lights but also requires you to run the power wire from the front. I thought the extra wire to the front was only for the brake controller but it is for the brake controller AND the tail lights.

One nice thing about the mopar harness is how everything was the perfect length and fit just right.

 

[TwoBobsKJ]

I added the supplemental harness as bob suggested and I now have working running lights on my trailers. Ended up only costing me $40 CDN because i found someone on ebay selling them for $6. Cost $30 to get it shipped to me but still better than the $75 the Canadian site wanted for the harness.

The install was not too bad just tedious feeding the wire through the panels to the front. Except for the get through the firewall part, that was annoying. I was trying to figure out how to nicely get the wire through it but there is just no good way to see the plug in the firewall from the engine bay. I ended up just pushing a coat hanger through blindly from the inside and then taping the wire on and pulling it back through.

Anyways glad to have proper lights on my trailer now. Thanks again Bob!

The problem was because I wanted a 7 pin plug to have the ability to do 7 pin or 4 pin. If you know you only want 4 pin there is a simple harness that plugs into the existing tail light harness and runs a 4 pin plug.

For the 7 pin harness from mopar, it plugs into the tail lights but also requires you to run the power wire from the front. I thought the extra wire to the front was only for the brake controller but it is for the brake controller AND the tail lights.

One nice thing about the mopar harness is how everything was the perfect length and fit just right.

Glad it worked out well - I like having factory as long as it's as effective as aftermarket.

AdamRoby, the 7-pin power contains a power lead that also provides power to the trailer, and not just for running lights and turn signals. It powers accessories in the trailer such as a battery charger for the trailer and lights inside the unit. The 7-pin powers the brake controller, on top of the running and tail lights. That's why there's 7 pins vs 4.

P.S. Unfortunately I've run into this same "Jeep Thing" on my Commander. We're going on vacation towing a travel trailer later this summer so I needed a brake controller. The XK has the tow package but I still needed to buy a supplemental harness and locate the brake controller wire and tap into the brake switch. Was the exact same process as I did on the KJ when I upgraded to the tow package on it :emotions34:

Bob