OEM 7 pin trailer harness HELP!

[Eric]

I just purchased a 2005 Expy XLT and after some research found out that the tow package the dealer told me my truck has is actually the "basic" class III package and not a HD package. As a result the vehicle only came with a 4 pin trailer receptical. However I have a boat with surge brakes and to back it up requires a receptical with a reverse lock out which is triggered by the back up light. I have attempted to locate the back-up light wire which according to a wiring schematic is black/pink. Without cutting into the harness covering to find it, I am unable to locate this wire. However in researching this issue online, it seems there is a factory harness under part number XL1Z13A576AA that could possibly be what I need. I have called 2 Ford dealers in my area and both parts departments found the part but were unable to tell me if it would work on my vehicle or how long the harness is as they don't have it in stock. Before I spend $145 for the part I thought I would check on this forum to see if anyone has any knowledge of this part and if it will fit my vehicle? I found the grey plastic square plug that the current 4 pin harness plugs into is about 6' to 8' long and is located on the left frame rail near the left rear door. It snakes around the back of the vehicle and up and over the rear suspension which is why it's so long, there are no other plugs between that plug I found the the 4 pin receptical.

Any help would be appreciated.

 

[tonydiv]

Just go to any Uhaul or RV place and they will have the proper harness.

 

[Eric]

Been there and done that, they do not have the proper harness. The Hopkins they sell has a black round pin with about 8" of harness, there is no such plug on my harness to attach this to. My harness has the standard 4 wires with one blue wire taped to it for use of electric brakes. I need the full 7 pin wired harness or I will have to break into the tail light harness burried somewhere in the interior compartment to locate the back-up wire and tap into that. I just can't believe Ford does not provide a full towing harness on all the Expys, most people buy these to tow with I would assume.

 

[KWT2000]

the 7 pin rv plug the center pin is an auxillary pin even on the superdutys its not wired up to anything because it can have many different uses from back lights to controlling a winch or just another positive wire to help keep up with demand on the trailer soo no matter what if you need to get signal from the reverse lights you have to wire it up

 

[tonydiv]

This is a good resource

http://www.etrailer.com/faq-wiring.aspx

 

[Eric]

Spent a few hours trying to figure this out. Thanks for the website link Tony, I had run across that site while searching for answers.

I plan on using the center pin for the back-up light wire, which is also the way they suggest on this website. I traced my 4 pin harness back and it terminates at a grey plastic square plug which is tucked up on the left frame rail under the left rear door area. The harness travels from there and snakes up and around the frame then a black wire comes off the harness and runs to the left rear disc brake, I assume it's part of the anti-lock brakes, there is a round plug for this wire. The harness then travels around the spare tire and ends at the 4 pin which is attachd to the hitch. The length of the harness is about 6 or 7 feet in total length. I assume that for the HD tow package they attach the 7 pin harness to this plug vs. a completely different harness from the engine compartment back.

If this is the case then this would be the part I'm trying to find as that would make it "plug & play" so to speak. I figue my only other option is to bust into the harness before this plug to find the back-up light wire and splice into it and zip tie a new wire to the harness and run it back, much cheaper way to go I'm certain, but requires cutting into a factory harness which can be tricky an no room for error.

Now to find a Ford parts dept. that can help me with this.

 

[Eric]

Here is a follow up, after going to 2 different Ford dealer parts dept's. I was unable to confirm if they have a 7 pin tow plug wire harness that plugs into the main harness. As such I discontinued that approach and I happened to be at a boating store called West Marine. Low & behold they had a 7 pin RV plug that is pre-wired to attach to a 4 pin flat. In addition it has additional stubbed out wires with heat shrink connectors for the electric brakes, auxillary, back-up light applications and ground. This allows me to plug directly into the factory 4 pin flat, then attach the blue trailer brake wire that was taped to the harness and connect my own back-up light wire from the main harness back and join to this plug. A fairly simple and not too expensive addition ($20 for the plug and extra wire).

 

[Tomfooter]

I've been watching your thread with interest. I have the same (4 Pin Flat) set up as you do. I don't need the larger connector (yet), but now I know what to do, if I do need it in the future. I know it was a lot of agravation, but I'm glad you got it worked out. I'm sure you helped a lot of others out, too. Thanks!

P.S. Now, what are you going to do for a (external) Transmission Cooler? I bet you don't have one of those, either! (if your Expy Is like mine) The bracket is there (in front of the radiator), but no cooler!

 

[Eric]

Ok here is an update. The Haynes manual I bought indicated in the wiring schematic that the back up light wire (which I need for the surge brake solenoid lock out) is black/pink. I took out the left rear tail light and confirmed the wire going to the bulb is in fact black/pink. However the amount of wire protruding from the rear body panel is not long enough to splice to. So I popped out the left rear package tray and it allowed me access to the wire harness. (By the way why Ford does not make that package area a storage compartment is beyond me as there is all kinds of open space in there). The package tray snaps in on 3 sides and you have to compress the sides to get it to unsnap, not at all hard to do.

Ok once I had access I cut about 2 " of tape off the harness and found the black/pink wire. I then put a "T" pin in it and had the wife put the car in reverse while I tested it with a volt meter, sure enough 13.3 volts when in reverse.

I cut away about 1/4" of the wire covering and soldered on a 14 gauge pink wire to it. Then I used liquid electrical tape over the splice and taped it back up. I then ran the wire along the harness and out the big factory rubber gromet at the tail light. I then ran the wire through some corregated wire covering to protect it and down to the rear of the frame and zip tied it top the 4 pin factory harness, and now I have what I need for my 7 pin plug.

As for the trans cooler, I looked and mine has 2 auxillary coolers in front of the radiator, one is a transmission cooler but it is small though, probably 12" by 4". My heaviest trailer is 5,000 pounds so I don't see it being an issue. Trans coolers are very easy to add, on my last truck I put one in and it was pretty inexpensive to do.

Hope this info helps!

 

[Tomfooter]

I'm glad your's is equipped a little better than mine. Yes, I'll have to install a cooler if I start towing any distance. For now, I only tow my Boat (abot 3,500 lbs.) for about 3 miles to launch it on weekends, and about 25 miles twice a year to store it. It sounds like you really did a good job on the wiring, though! Thanks for sharing!

 

[ChuckD]

The smaller one is the power steering cooler.

 

[Eric]

Correct, never seen a power steering oil cooler before. What is nice is that Ford still utilizes the trans cooler built into the radiator as well so essentailly you have the trans fluid traveling through the radiator as well as the external cooler, should be fine for most towing duties.