Installing a 7-pin trailer wiring harness

**sasksebring** · 07-03-2005, 01:30 AM

How to install the 7-pin Trailer wire harness in a Dodge Magnum.
---By Sasksebring

This took me about 2 hours to complete (including taking photos). I was surprised that it took me longer to install than the hitch itself. The worst part was drilling the two holes. I didn't have a very good hole cutter and it took a long time to get through the metal. I'd have to say it is moderate difficulty because of the drilling involved.

Here is the 7-pin wiring harness. Mopar part #82208926
Cost: $131.00 Canadian.
The end at the red arrow goes to the right taillight. The end at the blue arrow goes through the floor to the hitch.

I will probably only need the 4 pin trailer hookup, but this harness was only $15 more. The 7-pin to 4-pin adaptor costs just under $20. I decided that for $35 extra it was worth it for me to be ready for either hookup.
Here is the Mopar 7-pin to 4-pin adaptor:

The first step is to remove the upper cargo floor, then the cargo organizer and rubber liner if you have them. Then lift out the lower floor exposing the battery and spare tire.

View with lower floor removed:

Remove battery battery cables.

Remove rear panel by removing four Phillips head screws shown at arrows:

View with rear panel removed:

Remove spare tire. I ended up removing the jack as well to make it easier to drill the hole in the floor.

The panel behind the right taillight has to be removed. It pops off very easily. Just pry off from the close edge.

Behind the insulation is the access to a plastic nut securing the taillight. It is very difficult to reach unless you have tiny hands. I recommend a socket to remove it, as it has a hex head on it. Just be very careful not to drop it inside the car!

There are two more fasteners holding the taillight in place. They are a push in type plastic fastener and can be pried or pulled out. I don't have a special tool, so I used a pair of pliers and a rag to protect the plastic.

Then the taillight will pull out. Disconnect the wiring harness so you can set the taillight assembly aside.

**sasksebring** · 07-03-2005, 01:32 AM

A 1.75 inch access hole must be drilled about 2.25 inches over from the existing hole. This is the hard part. I hate drilling into a new car.

This is the bit I used. It took a long time, but did the job. Watch out... it gets HOT!

Watch when you are almost through and you might be able to keep the disc that you are drilling out from falling inside of the car. Maybe you'll learn from my mistake :-)
I'm just dreading the thought of this thing rattling around inside of the car! Grind down the sharp edges and paint some rust inhibitor on the bare metal.

Feed the wires behind the panel. I used a bent coat hanger to pull them through. You'll see in the picture that I had the wires between the panel and the insulation. This looked much easier. I would recommend trying to pull them up on the other side of the insulation (between the metal and the insulation), as it will make it much easier to get that grey snap-on panel to stay in place when you put everything back together.

The wire through the new access hole:

The wire connector tucked inside is the one your harness will splice into. Slide the small metal tab off the bumper cover and pull the wiring out.

This is where you are splicing into:

The harness connected. Seal the rubber plug in the hole with some RTV sealant or something similar. tuck the wiring away and reinstall the taillight assembly.

**sasksebring** · 07-03-2005, 01:34 AM

Now you must drill another 1.75 inch hole through the floor of the car. The hole should be centered on the angled area at the rear.

Again, paint on some rust inhibitor, feed the wiring harness through, and seal the rubber plug with some RTV sealant.

Feed the harness through the tab on the hitch, and plug in the round 7-pin receiver into the end.

Use the four supplied screws to secure the receptacle to the metal tab.

The Plugin is nicely hidden under the bumper.

I have seen some pictures showing the metal tab on the hitch facing straight out instead of angled like mine(see below). I am assuming that they changed this because the angled setup leaves more room for the wires and plug out the back (although it doesn't look as nice if you happen to be laying on the ground and are able to see it :-)
Part number of my hitch was 82207811AB. Maybe the AB stands for "Angled Bracket"?

Now attach the white lead to the negative terminal clamp and the red lead to the positive terminal clamp.

Now tuck away your wires, reassemble and you're done! I left that blue wire as it is. They give you instructions on how to run it to the front of the car for a trailer brake controller, but I know I won't be towing anything like that, so I left it there for now. Test your taillights and make sure everything works. Of course follow the battery reconnect procedure described in the knowledge base.

**DMAG** · 07-04-2005, 01:27 AM

EXCELLENT write-up!!!! A template for all further additions to the KB!! Bravo!

**oldschool** · 06-19-2006, 11:51 PM

Thanks for all the info! The part that stumped me on the factory instructions has officially been solved! Never knew what the blue wire was for!

oldschool

**Robins_SXT** · 06-20-2006, 03:47 AM

Great write up. I have the same kit awaiting installation but I didn't buy the factory hitch.

I'm still confused about the blue wire. The installation instructions have it run to the driver's side kick panel but leave it disconnected. I agree it likely has to do with controlling trailer brakes. My guess is that it has to be connected to the stop lamp switch. Vehicles that have factory wiring have a module behind the driver's kick panel that applies power to the trailer brake circuit. I'm assuming the big freakin module thats plugged into the kit wiring harness serves the same purpose in this kit.

I plan to trace the wiring in the kit harness and do some testing so I understand what it is that I'm putting in.

That's a big ball of wire this kit adds to the spare tire well. I'm thinkin some of it may fit under the power distribution center.

**oldschool** · 06-30-2006, 03:17 PM

Yep... I am that guy. Tired as hard as I could to put rags in the open area behind where the taillight is located to catch the hot disc I drilled out. And mysteriously I could not find where it went. It should have landed nice and safe and instead I think it slipped into the abyss of "impossible to find" nothingness in my rear fender. I am afraid to drive it now for fear of the "rattle-rattle" I may be faced with. Now I have to go hunt down a flexible magnet to do the search and rescue. I TRIED MAMA!

lolz great write up, brought it with me for the step by step. BTW the wingnut for the rear of the tail lamp is a 7/16" I believe.

Thanks!
matt

**sasksebring** · 07-19-2006, 03:20 AM

Originally Posted by oldschool

Yep... I am that guy. Tired as hard as I could to put rags in the open area behind where the taillight is located to catch the hot disc I drilled out. And mysteriously I could not find where it went. It should have landed nice and safe and instead I think it slipped into the abyss of "impossible to find" nothingness in my rear fender. I am afraid to drive it now for fear of the "rattle-rattle" I may be faced with. Now I have to go hunt down a flexible magnet to do the search and rescue. I TRIED MAMA!

lolz great write up, brought it with me for the step by step. BTW the wingnut for the rear of the tail lamp is a 7/16" I believe.

Thanks!
matt

Glad that I was able to help someone else out. This board has helped me so much!
Dave.

**thewagon** · 07-19-2006, 03:43 AM

Dave,

Only got 3 words for you...

You Da Man!

**djc208** · 07-19-2006, 10:10 PM

Originally Posted by Robins_SXT

Great write up. I have the same kit awaiting installation but I didn't buy the factory hitch.

I'm still confused about the blue wire. The installation instructions have it run to the driver's side kick panel but leave it disconnected. I agree it likely has to do with controlling trailer brakes. My guess is that it has to be connected to the stop lamp switch. Vehicles that have factory wiring have a module behind the driver's kick panel that applies power to the trailer brake circuit. I'm assuming the big freakin module thats plugged into the kit wiring harness serves the same purpose in this kit.

I plan to trace the wiring in the kit harness and do some testing so I understand what it is that I'm putting in.

That's a big ball of wire this kit adds to the spare tire well. I'm thinkin some of it may fit under the power distribution center.

The blue wire would hook to a trailer brake controller that is usually mounted up front so you can control the amount of brake bias to the trailer (how strongly the brakes respond). The brake signal is already provided at the back of the car.
As for the wires they actually don't take up too much room, the two big modules seem to fit nicely beside the battery/power module and the rest runs pretty much straight to the connection points. It's not too bad once it's all done. Just route the wires carfully, you only get one chance.

**L2C** · 05-09-2011, 10:03 PM

I used the exact same OEM kit in my '05 300C. The installation was very similar, except I did not have to drill a hole behind the left tail light - the connector is accessible behind the carpet in the trunk area. My installation was not as successful, however as my brake lights do not work when the harness is connected. I ony have the high-mount thrird lamp. If I un-plug the harness, all is well. Any ideas out there?

**All Show No Go** · 06-16-2011, 09:34 PM

Ok, I appreciate all the effort, but exactly why do I need to drill a hole behind the tailight ? The wiring harness is behind the rear bumper fascia, why can't I just take the tail lights out, as demonstrated, tap into the harness there, and tie strap the trailer harness to the existing harness. Saves a lot of holes in the car body, that I too, am reluctant to drill.