Hidden trailer electrical connection

[jimbo486]

About a month ago, I installed a B&W receiver hitch. Since then, I've been working at building a harness for trailer connections, one inside the bed for a 5th wheel and one at the rear bumper somewhere for a conventional tow. I wanted to find a centralized location near the pivot point of both the truck and trailer. As well as finding a location higher than mounted down on the hitch itself where the possibility of it dragging or catching on something would be greater, potentially tearing out the plug and wiring with it. Also, in the even that I launch a boat, it won't have a chance of being submerged or getting too wet.

I began my search thinking about the older model cars with fuel tank filler necks behind the rear license plate. After a lot searching, I stumbled across a license plate flip kit for roll pans, made by Pilot. [ame="http://www.amazon.com/gp/product/B000BQQN2M?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00"]Amazon.com: Pilot FLP001 License Plate Flip Kit For Roll Pan: Automotive@@AMEPARAM@@http://ecx.images-amazon.com/images/I/41WvLN4IKoL.@@AMEPARAM@@41WvLN4IKoL[/ame]

At the time, it was going for $12. After shipping and taxes, it was $20. I had it in my hands about a week ago. You may already see where I'm going with this. Yesterday, I took some time to figure out how I would install it. I did so with it oriented as a flip down.

Rather than spending time with a tape measure and attempts to center it horizontally and vertically, I simply put a 3/8" bolt through the "top" squared holes (which would be used to attach the plate) of the bracket and the bumper and tightened them. 3/8" was the exact size of the both sets of holes which allowed for a near perfect positioning of the bracket. With the bracket temporarily in place, I used a 5/16" drift punch to mark the position of the holes for the hinges. I removed the bracket and drilled 2 - 5/16" holes where the drift punch had marked. Deburred and chamfered the holes and mounted the bracket to test it's function.

It works great! I'm curious about removing the springs and removing a couple of coils from both to lighten the tension some but it's not terrible. I'm just thinking of the pressure it might put against a trailer plug and possibly causing intermittent connectivity. No way of knowing until I can test it.

The reason I mounted it in a flip down orientation was because the hinge holes would've been just below and right next to the square holes in the bumper which would've just made them oblong.

With that done, I used a bracket for a 7-way plug to trace the hole required to be cut. The bracket's opening measured 2 1/8". Lucky me, I only had a 2" and 2 1/2" hole saws. I measured the plug to be used with a set of calipers and came up with a minimum dimension of just over 2". I used the 2" hole saw and assumed it would take some filing to open it up just a bit more to clearance for the plug. Turns out, while drilling, the hole saw walked just enough along its radial axis that it made for a hole sized a touch over what I measured. The plug slipped right in place. I opened the 4 holes in the plug flange to a more common 1/4" size. With the plug held in place, I used a 1/4" drift punch to mark their positions, removed the plug and drilled 4 - 1/4" holes through the bumper. Using 1/4" stainless hardware, I mounted the plug and did the same with the license plate bracket using 5/16" stainless hardware.

As it sits, I can live with it. The plate doesn't stick out an excessive amount in my opinion. I would like to see if there are any plugs that have a slightly lower profile than the one I used. Another thought that just came to mind is the possibility of building a small recessed box which would allow for the plug's cover to sit flush with the bumper face. There's room for improvements. No complaints though for only having $20 in it.

 

[BRE]

I can dig it!!
Way to think outside the box a little.

 

[6 speed 90]

I like it!!

 

[oldestof11]

I wonder if you can put in a little rod that flips down and locks the plate down so it doesn't ride anywhere on the plug.

 

[TheBac]

Very nicely done.

Interesting idea, oldestof11.

 

[jimbo486]

Thanks guys.

I wonder if you can put in a little rod that flips down and locks the plate down so it doesn't ride anywhere on the plug.

Good idea, Jon!

 

[DISTURBED]

Do you have a front plate? Only concern I would have is what the police would say if they couldn't see the plate and how much harassment you will get from it not being visible when using the plug.

 

[jimbo486]

I do have a front plate. I did wonder the same initially which is why I wanted to mount it as a flip up. That way, if I am stopped with a trailer in tow, the officer could still see the plate. It wouldn't be much hassle to get out and unplug the trailer to flip the plate back up for him or her to see.

 

[oldestof11]

But then you run into improper trailer lighting if they let you go.

 

[jimbo486]

Haha but of course I'd plug it back in! Maybe I'll look into a way to get it mounted in a flip up orientation. I had initially figured I'd make an adapter for the upper bolt holes out of flat stock and just weld the hinges to it. I could probably make it happen or just oblong the upper holes.

 

[jimbo486]

I finally had a chance to make all of the electrical connections. Both the plug inside the bed and at the rear bumper have been wired in series with each other and each pin in both plugs gets the proper signals as verified by a test light.

I used Delphi Weatherpack connectors at both plugs for ease of removal. I forgot to get a picture of the connectors for the plug in the bedside but it looks the same.

In the following picture, looking forward, you can see the 2 wires becoming one and supplying voltage to the rear plug. One of the 2 wires comes from the Curt T-connectors in left and right rear taillight harnesses. The other of the 2 wires runs forward and up to the plug in the bedside. The standard for RV trailer wiring lists Green = Right turn signal, Yellow = Left turn signal, Brown = Running lights, White = Ground, Red = 12 volts from battery, Blue = signal from the trailer brake controller and Purple = Reverse lights (optional). I've never run across any but it's not often that many trailers have reverse lights so for now, I left it capped until I can tap into the factory 4-way square connector for a reverse light signal.

Curt T-connectors #55317 specifically for '86 to '94 Dodge trucks (according to Curts application chart). Passenger/Right side has the green wire for your right turn signal. The Driver/Left side has the brown and yellow wires for your running lights and left turn signal, respectively. I cut the 4-way flat plug off leaving about 6" of wire for future use, if any.

Here is the Passenger/Right side Curt T-connector installed. I didn't take a picture of the Driver/Left side as it looks identical, just with 2 different colored wires for different purposes, of course.

Lastly, looking up at the frame crossmember showing the common ground point (for a few things). From right to left (if it really matters that much): Ground for the solenoid on my air horns, White being a chassis ground for the trailer lighting and accessories, ground for the trailer running light relay, and a ground for the air compressor relay mounted to the inside of the driver side frame rail.

As well as an obvious relay which is specifically for the trailer plugs. Dodge issued a TSB years ago for those who were burning up their headlight switches while towing a trailer. The simple fix and good idea was a relay to relieve the switch of the additional current draw/load from the trailer lights.

Coming in from the lower right corner of the picture, you can see the yellow and brown wires from the Driver/Left Curt T-connector. Yellow being the left turn signal runs over and into the 'Y' which then supplies both 7-way plugs.

The brown wire being for the running lights runs into pin 86 and out from pin 87 (see the loop) and to the 'Y' which then supplies both 7-way plugs. Black (marked with red electrical tape) being constant 12 volts (+) from the battery into pin 30. The looped black wire is from pin 85 to ground.

All I have left to do at this point is wrap everything in split loom cable wrap. I'll use a length of inner tube for the rear plug and wiring having it ziptied tightly to the body of the 7-way plug and wrapped up to the highest point with the hopes of preventing water from getting in and possibly corroding any connections within the plug.

Hopefully this thread can provide some kind of help to anybody wanting to add a trailer plug to their truck or any vehicle, if it hasn't been done already.

 

[camarokiller]

Like the inner tube idea. Pack it full of grease and i'd bet youd never have a connection issue.

Im gonna use the same plate mount(mine has to flip up, no front plate) for my custom hitch to come through my roll pan. I may stick the plug behind the plate too.

 

[jimbo486]

Correction needed for the description of the last picture in my previous post. The grounds are listed in order from left to right, not right to left. :1tooth:

 

[Badbrad3701]

Do you have a front plate? Only concern I would have is what the police would say if they couldn't see the plate and how much harassment you will get from it not being visible when using the plug.

If u are using the plug there's gonna be trailer on so there not going to see it anyways

 

[DISTURBED]

If u are using the plug there's gonna be trailer on so there not going to see it anyways

I've been pulled over and had them check to see if the truck has both plates. You can see the rear plate pulling a tag along.

 

[jimbo486]

I do have a front plate as per CA requirements. The rear plate has the registration tag on it however, the front does not. As stated, I'm going to look things over again and see about changing it to a flip up orientation. That way with a trailer in tow, an officer could easily see the plate and wouldn't bother stopping me so that I could disconnect and flip the plate back up.

 

[jimbo486]

I was able to easily change the bracket to a flip-up orientation. All I had to do was widen the original mounting holes for the license plate. A square file had it done in 5 minutes.

I wonder if you can put in a little rod that flips down and locks the plate down so it doesn't ride anywhere on the plug.

This will be the next thing I do in order to prop up the plate and prevent any unnecessary tension on the trailer plug.

Leaving Wednesday morning destined for Payson, AZ to bring home a 1987(?) StarCraft 28ft. pontoon boat.

 

[4x4dually]

Under one or both of the little bolts that holds the plate to the flipper on the bottom, screw a flip down bar on them. Then when you flip the plate up, the bars drop, and hold the plate up off the plug. Then just lift the plate, tuck them up, and it will close back down. Just an idea.

 

[Chris Tobin]

Insulate the bottom edge of the plate in case it comes down while towing so that it won't rub and cut through the trailer wires. You can use the insulation from a length of 8- or 10-gauge wire stripped off the wire then sliced long ways with a razor then slid onto the bottom edge of the plate to prevent the sharp edge of the metal plate from cutting/chaffing against the trailer wires.

 

[jimbo486]

Good idea as well, Chris. I have a ton of short lengths of braided fuel hose that I could use to accomplish that. Plus, it would prevent any cuts on your fingers. I've already had a couple.