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Tech: Trailer plug wiring

 
 
 
 
  #1  
Old 02-05-2009, 05:15 PM
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Default Tech: Trailer plug wiring

This is the method I used to sort thru my trailer wiring. Trailer wiring and electricity seems to strike fear in the hearts of the bravest DIY, so maybe this approach will ease the pain and work for you as well. Most of us tow trailers, but not all of us are electrical engineers or have a degree in electronics.

What prompted this write up was the plug for my trailer was damaged and in need of replacement. Even though I built the trailer and wired it, I approached the task as if I had no prior knowledge of the wiring. So let’s get started!

One thing you need to do is forget about the “Color Code” of the wires. Electricity does not care what color of insulation is on the wire you or someone else used. So why should you? Knowing a “Color Code” will only help you if someone else knew it and adhered to it. Color Codes vary from manufacturer. What is important is the position and function of the wires in both the receptacle and the plug, and that BOTH of them match.

I like to start sorting the mess out at the beginning; you need to know the “Pin Out” for your truck receptacle. I’m not sure when they started doing it, but Dodge put the pin out for their trailer plug receptacle right on the cover. The pin out is standard, the wire colors are not.
Here is a pic of my receptacle cover on my truck.
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On it, it tells me which connection point is used for which function. (How handy is that!)
So, to get my trailer electrical functions (Lighting, Brakes, etc.) to do what I want, all I have to do is match up the positions and functions of the plug to the receptacle.

Now, my trailer is parked in the back yard, behind a gate, the motor home, the Jeep and the work truck. My truck is parked out front, under the carport.
No problem! The two don’t have to be anywhere near each other to get this right. I make up a diagram of the pin out of my truck’s receptacle.
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Next, I put the plug over the top of the diagram I made.
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I now have a reference of how my wiring should terminate to the trailer plug.

Now it’s time to start sorting out the wires. Remember to slide the plug housing over the wire cable before beginning. The first thing you need to determine is which wire is ground. In a modern automotive application, the Negative battery potential is applied to ground. (You knew that, right?) So, whatever it takes, find the ground wire attached to your trailer.

I use a small 12-volt battery to sort out the wiring on trailers. (Mine, my family, my friends, etc.) You can use a spare automotive battery or any other 12 V power source.

Connect the ground wire to the Negative terminal of the battery. In my case, it was the White wire as shown in the Pic below. The reference to color is for visual reference only.
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If you have all same color wires, or several duplicate colors, you can still do this! Make up some tape tags.
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Writing info on the tape is easiest while it is still on the roll, BTW.
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Once you determine which wire is ground, mark it with a tape tag.
Connect it to the negative battery lead.

Now, pick a wire, and apply it to the positive of the battery. For visual reference, I chose the yellow wire.
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Observe your trailer for an indication of function. Again, for visual reference, the left Tail Light came on.
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Either write down the color of the wire and what function it performed, or attach the tape tag to the wire, depending on your situation.

Select the next wire and repeat the process. Once again for visual reference, I chose the brown wire.
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Observe the trailer for an indication of function. In my case, the Tail/Running lights came on.
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Again, either write down the color of the wire and what function it performed, or attach the tape tag to the wire, depending on your situation.

Select the next wire and repeat the process.

When you are finished, you will have all wires marked as to their function, or a list of the color and their function for reference.
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Next, place your trailer plug over the diagram of the receptacle, and using either your tape tags or your list, terminate the wiring on the plug.
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Last edited by wildcat; 02-05-2009 at 05:19 PM.
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  #2  
Old 02-05-2009, 05:16 PM
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Assemble the trailer plug to it’s housing, tighten the plug locking screw, and the cable strain relief screw.
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As a final test, couple the vehicle to the trailer, and check all functions for proper operation.

That’s it!

As always, any questions or comments, feel free to post them up!
 
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Old 02-05-2009, 05:17 PM
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Right on Very Nice Job Here !
 
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Old 02-05-2009, 11:09 PM
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Great writeup. the diagrams can also be found at Husky Trailer. I hate it when I get a trailer that has been "custom wired" There are standard wireing diagrams for 4wire, 6 wire and all others. Wildcat has a good plan there, as long as your truck plug isnt "custom wired" If your trailer plug on your truck has more than a few feet of electical tape, or a few pounds of wire nuts, you might want to unravel the ratsnest and do it right.
Thats good that Dodge put the diagram on the plug.
 
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Old 02-06-2009, 03:40 AM
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I see what you are saying color is not always correct. But, there is a color code that coincides with function and wire sizing.
If you buy wire designed for trailers; the battery(bk.), brake(bl.) and ground(wh.) conductors are larger cms than lighting circuits. If you don't use trailer wiring consider a cable with large enough conductors to handle the load.

more importantly, what's on the trailer?
 

Last edited by Hut; 02-06-2009 at 03:43 AM.
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Old 02-06-2009, 08:53 AM
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Originally Posted by Hut View Post
If you don't use trailer wiring consider a cable with large enough conductors to handle the load.

more importantly, what's on the trailer?
Absolutely!

My Rock Buggy. Haven't you seen pics?

This one is in my Album:
https://www.dieselbombers.com/member...1-my-buggy.jpg
 
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Old 02-06-2009, 11:13 AM
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good job man . tell the guys where you got plus on plug is battery chargin wire and they could wire up camper good job
 
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Old 02-06-2009, 01:01 PM
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Originally Posted by wildcat View Post
Absolutely!

My Rock Buggy. Haven't you seen pics?

This one is in my Album:
https://www.dieselbombers.com/member...1-my-buggy.jpg
Very cool!
 
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Old 02-07-2009, 12:36 AM
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IF YOU HAD TO WIRE A WINCH AND BATTERY INTO YOUR TRAILER WIRING, HOW WOULD YOU DO IT??? I WANT TO DO THIS ASAP SO I HAVE CONSTANT BATTERY/POWER TO THE WINCH WHEN CONNECTED.
 
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Old 02-07-2009, 12:38 PM
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I have no idea about the actual winch so this may not be sufficient.
#10 black from pin #4 on 7 pin connector to positive battery post(mounted in box) Fuse holder & appropriate size wire from fuse to winch. assuming the winch is 12v and has integral controls.
Ground to frame with equal size wire.
A nice thing to do is add a solar powered trickle charger to help keep the battery charged.

Not sure if this helps or not...
 

Last edited by Hut; 02-07-2009 at 01:09 PM.

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