7 way trailer plug

My boss swears there are two ways to wire a 7 blade RV plug, one for rv's and another for other trailers. Anyone else ever heard that, I never have?

I know 6 way round have 2 patterns, with the auxiliary and brake wires switched, and 7 post semi plugs are different, having a dedicated brake light circuit. But I've only seen one way to wire a 7 blade RV plug.

There is two ways to wire them sometimes between different truck manufacturers they will be wired one way or the other

There are 2 ways to wire a 7 way plug:
RIGHT
and
WRONG
All of the trailers with a 7 way plug that I have bought new in the last dozen years or so were all wired the same. Including the Rvs.

One way to wire them as all vehicles are the same. But the wire colors are usually different between rv's and regular trailers. The terminals still do the same job.

It seems that before trucks came from the factory with a trailer package some people wire them to suit themselves. If my math works right there are 49 possibilities and 48 would be wrong.

Yep, confusion reigns on that subject!

There are 2 ways, not sure what differentiates the application. Then to add more confusion, the color markings inside the plug can disagree between brands.

I generally match the trailer to the vehicle. Chances are the vehicle is already paired up to other trailers.

The correct way is to wire it so the trailer and the truck are in sync. Can't be done unless you have both the truck and the trailer.

(quoted from post at 23:33:23 04/08/19) My boss swears there are two ways to wire a 7 blade RV plug, one for rv's and another for other trailers. Anyone else ever heard that, I never have?

I know 6 way round have 2 patterns, with the auxiliary and brake wires switched, and 7 post semi plugs are different, having a dedicated brake light circuit. But I've only seen one way to wire a 7 blade RV plug.

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There's two color schemes (and more) for the wires in trailer pigtails, that may be where his idea came from.

Dont know about a law that says they have to be wired a certain way or with certain colors. Most manufacturers have adopted a standard way and colors but not all. On an old trailer its anybodies guess.

I have been selling and installing trailer hitches, brake controls and wiring electrical plugs since back in the early seventys. Probably have wired thousands. Ford, GM and Dodge have used the standard 7 prong plug wiring code for years. Most of the good trailer manufacturers also use that code. The color of the wires going to the plug means nothing. The code markings on the back of the plug is the Key. Left turn--Red
Right turn-Brown
Running lights -Green
Ele Brake--Blue
Aux 12V--Black
White --Ground
Center Pin-Yellow--Back-up Lights-Everyone thinks this is the ground- IT IS NOT!!!
This code was developed by the RV industry many years ago. IT is for the plug with 6 flat pins and a round center pin. This is the code used by all the new vehicle manufacturers. If you wire your trailer any other way than this, you will have problems. Now if you decide to go with the plug that has all round pins, like used on a class 8 tractor and trailer the code is different.

Ok, the different color schemes within the same pattern are probably what he's thinking. Unless it only has 4 wires running to the plug (signals, markers, ground) I don't trust any color scheme, and even then double check.

When he borrows the neighbor's trailer and the cord is hanging off the neck with no plug, I just grab a battery and test leads and start working out which wire powers which function.

I was a used Truck/Tractor/RV dealer for years and can tell you FOR SURE I saw many many wired different ways, IT DOES AND CONTINUES TO HAPPEN. A lot of the difference I observed depended on the connections for backup lights and 12 VDC auxiliary power (say for toad battery trickle charge or trailer dome lights). NOTE Im NOT saying any were right or wrong, Im ONLY saying over many years and a ton of vehicles I saw different wiring......

As posted THE TWO VEHICLES MUST MATCH for the system to work.

HOWEVER nowadays I see most wired as Bob's picture indicated for RV's and that's how I wire my RV and any toads I pull. On the back of many pickups the 7 pole receptacle and wiring diagram is posted right on the receptacles.

The 6 pole what I call horse trailer plugs were more notorious for using two different wirings. Their difference concerned what pin was used for 12 VDC aux power to run the trailers inside dome light. RV dealers even sold two different 6/7 adapters depending on what pin was used for 12 VDC

John T

I was confused the first few times I had to rewire the 7 pin flat plug on my trailers.
Industry standard long before the RV 7 wire flat pin plug was even thought of was
Yellow wire - Left turn
Green wire - Right turn
Brown wire - Tail lights

RV mfg's decided not to use that standard and used those colors for different functions.
Yellow wire - Reverse lights
Green wire - Tail lights
Brown wire - Right turn
The average guy wires by color and doesn't take time to write down what wire came from where when they take the wires out of a broken plug, or worst yet is trying to rewire the plug after the wires have been yanked out.

Guy replaces a cracked plug on his RV following the digram that came with the new plug, when finished everything works "YEA", walks back to the utility trailer hooked to the RV and finds the wires ripped out of the plug. No big deal just wire it up exactly like the instructions showed on the plug they just finished wiring, when they get done nothing works right and their like "What the H", I just wired the RV and everything works perfect, why won't the lights on this stupid trailer work.
Personally I think the RV industry should make those 3 wires match the rest of the industry.
Also the utility trailer industry should change that dumb purple wire to red, every after market 7 wire cord I've found has a red wire and no purple.

Rant over.

Moonlite ...for sure we had different math teachers in school but I dozed off a lot. So seven wires gives you 7 color choices for the first pin, then you have 6 wires left as possible choices for the second pin, 5 for the third pin and so on until you run out of wires and pins. I think (not sure) that gives a guy 7x6x5x4x3x2x1 = 5040 different possibilities or combinations ..... I think I remember something called permutations and combinations. This link below gives an explanation of seven different letters, he does get off track a bit but eventually comes out to 5040. I wouldn't want the task of proving it, probably eat up a weekend or two.
Untitled URL Link

I went to school with someone whose family just wired the plug on the pick-up when they bought it. Same thing with their trailers. Each pick-up had pigtails behind the seat to make each trailer work with it.

Yeah.