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Old 08-13-2016, 11:48 PM   #1
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Yellow wire/7 way cord

Hi all have a question regarding the yellow wire in a 7-way cord. When pulling away from the 5th wheel felt a tug and found the 7-way had hooked on the 5th wheel hitch.
Well after putting everything back together and figuring out what wire went where I had one wire left over. From what I can find this yellow wire is supposed to be an auxiliary power wire, however it only gets power from my reverse lights and it was hooked to something as the insulation around the end of it has heated up (thankfully no blown fuses) and the trailer has no reverse lights. The wire has been capped off for now.
Any suggestions would be greatly appreciated.

Thanks,
Curt
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Old 08-14-2016, 04:04 PM   #2
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The center pin is usually dedicated for reverse lights or camera power. If you have neither of those on the RV then it shouldn't be connected to anything on the RV.

You can check the resistance of the yellow wire on the RV to make sure it isn't shorted and if it's powering something. If it's powering something you can apply power to it and see what turns on.
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Old 08-14-2016, 04:09 PM   #3
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Here you go!

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Old 08-14-2016, 10:30 PM   #4
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Bama and Herk, Thank you for the reply but I'm even more confused. With luck below you should see a picture of what I at the time was running off of.

The trailer itself only has 3 wires that are color coded properly white, black and blue. All the rest are a brown color and I had to probe and use jumpers to figure out what went were and what powers what. Everting thing is working properly signals, brake lights, ect.

The yellow wire coming out of the 7-way and going to the trailer only has power when TV is put in reverse. I'm guessing the reverse lights are powering this. Also the yellow wire was hooked to something on the trailer as the insulation at the end of the wire shows signs of over heating.

Both the trailer and TV are wired from the factories no type of modifications have been done that I'm aware of.
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Old 08-15-2016, 12:07 AM   #5
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Yellow is for reverse lights. It's the center pin on the plug. I'm not sure what your confusion is. If you don't have or want any backup lights then don't use it.
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Old 08-15-2016, 12:37 AM   #6
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Curt:

Herks drawing shows the wiring colors in the umbilical cord you plug into your tow vehicle.

If you open up the junction box that the umbilical cord is routed to, I believe you will find that the colors will change to the ones in your pic.

In other words, the Tow Vehicle/Plug colors are not the same as the actual wiring in your TT from the junction box to all the lights, etc.

I ran a standard 4-pin connector from my rear bumper to the junction box to power the LED's on my bike rack. The TT lights' wire colors were not the same as the umbilical cords wire colors. I wrote them down, but they're in the TT in storage at the moment, so I can't tell what they are.

I've attached a pic of the 4-pin wires, not that it helps much.
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Old 08-15-2016, 04:42 AM   #7
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Originally Posted by 05CrewDually View Post
Yellow is for reverse lights. It's the center pin on the plug. I'm not sure what your confusion is. If you don't have or want any backup lights then don't use it.
First off .NO ONE IS REALLY WRONG... there are several different 7 pin trailer wiring configurations where the "yellow" wire is designated for different things.

The 7-wire traditional - the yellow wire is the "left turn/stop" lights
The 7-wire standard - the yellow wire is the "reverse" lights
The 7-wire heavy duty - the yellow wire is the "left turn/hazard" lights

Then of course there is the "DONT HAVE A CLUE" were some do it your self fool didn't take the time to follow a wiring diagram and only the lord really knows what color is for what.

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

Every Rv'er should have one of these simple 12 volt testers in their tool bag.
connect the lead wire to ground, touch the probe on the hot wire, if its hot the light glows.
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Old 08-15-2016, 05:28 AM   #8
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Originally Posted by Curt and Michele View Post
Bama and Herk, Thank you for the reply but I'm even more confused. With luck below you should see a picture of what I at the time was running off of.

The trailer itself only has 3 wires that are color coded properly white, black and blue. All the rest are a brown color and I had to probe and use jumpers to figure out what went were and what powers what. Everting thing is working properly signals, brake lights, ect.

The yellow wire coming out of the 7-way and going to the trailer only has power when TV is put in reverse. I'm guessing the reverse lights are powering this. Also the yellow wire was hooked to something on the trailer as the insulation at the end of the wire shows signs of over heating.

Both the trailer and TV are wired from the factories no type of modifications have been done that I'm aware of.
I just changed plugs and left the yellow wire off the center terminal, I don't have reverse lights. All works fine. Either call etrailer or hopkins they will help you out. If you hook the yellow wire up your reverse tail lights on the truck will come on when you turn on your left signal light. Your TV reverse lights will blink at the same time. Just put a hopkins replacement on last week, Your TT might be different, they never wire two the same. They call it a 7 pin connector but you only use 6 wires. NOT THE CENTER TERMINAL...
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Old 08-15-2016, 07:50 AM   #9
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Quote:
Originally Posted by ShermanD View Post
First off .NO ONE IS REALLY WRONG... there are several different 7 pin trailer wiring configurations where the "yellow" wire is designated for different things.

The 7-wire traditional - the yellow wire is the "left turn/stop" lights
The 7-wire standard - the yellow wire is the "reverse" lights
The 7-wire heavy duty - the yellow wire is the "left turn/hazard" lights

Then of course there is the "DONT HAVE A CLUE" were some do it your self fool didn't take the time to follow a wiring diagram and only the lord really knows what color is for what.

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

Every Rv'er should have one of these simple 12 volt testers in their tool bag.
connect the lead wire to ground, touch the probe on the hot wire, if its hot the light glows.
I don't know why you're quoting me. I'm not saying anyone's right or wrong. I gave the best logical answer to there problem, which was further explained in their post #4.
All the other variables in trailer plug wiring info is TMI and I can see now how they can get confused.
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Old 08-15-2016, 07:54 AM   #10
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If the center pin is connected to something and you don't have reverse lights or a backup camera, then we can't tell you what it may be hooked to. And there is a possibility that it isn't hooked to anything, but got temporarily shorted and that's what caused the insulation to melt.

You should be able to open up the junction box under the RV and see if the yellow wire is actually hooked to anything.
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Old 08-15-2016, 08:27 AM   #11
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Originally Posted by 05CrewDually View Post
I don't know why you're quoting me. I'm not saying anyone's right or wrong. I gave the best logical answer to there problem, which was further explained in their post #4.
All the other variables in trailer plug wiring info is TMI and I can see now how they can get confused.
Yellow is for reverse lights. It's the center pin on the plug. I'm not sure what your confusion is. ,,,,,that's why

Maybe you should have read my entire post instead of assuming because there are THREE DIFFERENT 7 wire CONFIGURATIONS and YELLOW is NOT ALWAYS the REVERSE LIGHT WIRE
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Old 08-15-2016, 09:42 AM   #12
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Quote:
Originally Posted by ShermanD View Post
Yellow is for reverse lights. It's the center pin on the plug. I'm not sure what your confusion is. ,,,,,that's why

Maybe you should have read my entire post instead of assuming because there are THREE DIFFERENT 7 wire CONFIGURATIONS and YELLOW is NOT ALWAYS the REVERSE LIGHT WIRE

I know that but it doesn't pertain to the OP. Go back and read post #4.
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Old 08-15-2016, 09:49 AM   #13
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Originally Posted by 05CrewDually View Post
Yellow is for reverse lights. It's the center pin on the plug. I'm not sure what your confusion is. If you don't have or want any backup lights then don't use it.
You are correct according to my wires the yellow to the center will work both your left signal and reverse tail lights if you hook it to the center pole. Just leave it capped off and don't hook anything to the center pole, it will back feed.... PS: do not use the standard TT wire diagram. OP I can copy how I hooked mine up if needed. you only use 6 wires.
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Old 08-16-2016, 10:19 AM   #14
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Originally Posted by rockfordroo View Post
Curt:

Herks drawing shows the wiring colors in the umbilical cord you plug into your tow vehicle.

If you open up the junction box that the umbilical cord is routed to, I believe you will find that the colors will change to the ones in your pic.

In other words, the Tow Vehicle/Plug colors are not the same as the actual wiring in your TT from the junction box to all the lights, etc.

I ran a standard 4-pin connector from my rear bumper to the junction box to power the LED's on my bike rack. The TT lights' wire colors were not the same as the umbilical cords wire colors. I wrote them down, but they're in the TT in storage at the moment, so I can't tell what they are.

I've attached a pic of the 4-pin wires, not that it helps much.
Agreed. ...there seems to be no consistency from the TV plug to the junction box. These trailer folks seem to have complete disregard for wiring codes and colors. I've added some extra signal and marker lights to my TT and have done the same...started my own code as notes in my phone!
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Old 08-16-2016, 07:34 PM   #15
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The Y wire in my CC-29RE was capped inside the front storage area.....I extended this wire with Y wire to the back of our 5er.....Installed a backup beeper unit and also a LED backup light on drivers side of 5er......J
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Old 08-17-2016, 10:28 PM   #16
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Originally Posted by Bama Rambler View Post
If the center pin is connected to something and you don't have reverse lights or a backup camera, then we can't tell you what it may be hooked to. And there is a possibility that it isn't hooked to anything, but got temporarily shorted and that's what caused the insulation to melt.

You should be able to open up the junction box under the RV and see if the yellow wire is actually hooked to anything.
And that's were my problem lies, I pulled the cord out of the junction box and in the junction box is nothing but brown wires, except for hot, ground and electric brakes.

Maybe I should not have put this under Tow Vehicle but figured if I could positively figured out what the yellow wire coming off the TV may go to I could trace it down some how.

Once again Thanks everyone.
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Old 08-18-2016, 02:26 AM   #17
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I just replaced my cord, the yellow wire from your TV is for the center post or revise light, on your trailer the yellow wire is capped off in the box the cord ties into, just did this yesterday.
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Old 08-18-2016, 02:30 AM   #18
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White and black are power from your Trailer
Red and brown turn signals, blue is brake ,green is running lights. That is the way mine is wired.
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Old 08-18-2016, 06:25 AM   #19
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Originally Posted by Curt and Michele View Post
And that's were my problem lies, I pulled the cord out of the junction box and in the junction box is nothing but brown wires, except for hot, ground and electric brakes.

Maybe I should not have put this under Tow Vehicle but figured if I could positively figured out what the yellow wire coming off the TV may go to I could trace it down some how.

Once again Thanks everyone.
I understand your confusion. Once you got to the junction box all bets are off because all the wiring to the lights are the same color wires. I think mine is like that too. However you said that everything is working except that you can't figure out what the yellow wire on the umbilical cord is supposed to do. that's why everyone is concentrating on the yellow wire.

Can you take a picture of the wires in the junction box? I know it'll be a challenge, but I think it'll be worth it.

Here's another thought. Is the end of the yellow wire tinned (filled with solder)? If it is then that could be why the insulation is melted. They could have done it when they tinned it.
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Old 08-18-2016, 06:54 AM   #20
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Originally Posted by Curt and Michele View Post
And that's were my problem lies, I pulled the cord out of the junction box and in the junction box is nothing but brown wires, except for hot, ground and electric brakes.

Maybe I should not have put this under Tow Vehicle but figured if I could positively figured out what the yellow wire coming off the TV may go to I could trace it down some how.

Once again Thanks everyone.
If all of the wires are currently disconnected, and you have a volt meter, separate the pigtail wires, strip and tape them individually and plug the pigtail into the truck.

Using a volt meter on VDC (or DCV in this case), monitor all the trailer side wires for the one with 12 volts. That wire goes to the trailer battery and needs to go to the red wire coming from the pigtail. Mark and tape a tag to it.

Next, meter the voltage on the pigtail yellow wire. Turn on the left turn signal and if the yellow end goes to the truck's left turn signal, the voltage should swing between zero and 12-13 volts or so (you may need the truck running).

If so, using a short 5 amp FUSED jumper wire from the yellow wire, test each brown end in the junction box to see what turns on. If you find the ground wire by mistake the 5 amp will open before any damage is done to the truck. Label the wire with a small tape tag.

Repeat with the right turn signal.

Turn on parking lights and identify the wires going to the marker lights.

NOTE: depending on how your side and top marker lights are wired, 5 amps may not be enough to handle them all if there is only one wire to all of them. The some incandescent bulbs can draw up to 1.2 amps each (LEDs draw MUCH less and 5 amps will always work regardless of how the markers are wired). If the markers draw more than 5 amps, identify all of the other wires first before increasing the fuse to 7.5 amps and then to 10.

The brakes and ground wires will always be "cold" until someone taps the brakes in the truck. Then the brake wire from the truck will show some voltage. The easiest way to identify the brake wire from the trailer side by pulling the breakaway momentarily (long enough to take a reading) as the trailer battery will be sending power on that wire when the break away is pulled. Be quick about it as the brakes will be pulling full power from your battery and may overheat if left on too long (no more than 5 minutes as you will also be running your trailer battery down).

Once you have identified all the correct wires, write down the color code/tag numbers for your particular camper.
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