Wiring troubles

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purple haze

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Jul 13, 2019
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Hi all.  I have 2014 Eclipse toy hauler that I got new. A few weeks ago, I picked up a 99 F250 pretty much just for towing the t.h. So, today, I decided to hook up the trailer to see if the lights, brake controller, etc all work, in order to avoid any last minute surprises. When I plugged in the 7 pin connector I got smoke rolling out from under the bumper. I figured that there was a bare wire touching metal. I picked up a new plug, hooked it up and the same thing. Although, not as much melted wire, as I was prepared to unplug, which I did. The hot wire on the truck end of the plug (the terminal at the 1 oclock position) is what melted away the insulation. Now that terminal is supposed to be hot whether the key is on or not, right? I then checked the mating terminal on the trailer w/o the truck hooked up and it has power to it. The trailer is unplugged from the 110v house current. That seems odd to me that 2 wires that have power connect together. I talked to a tech at the r.v dealer and he says that there is a problem in the trailer wiring. Maybe a loose wire in a junction box. Idk, But, I've towed this trailer with 3 different trucks and never had such problems.

 

grashley

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Welcome to the Forum!

From the trailer side, that #1 pin is connected to the battery, so if the TT battery is connected, it is hot.  The other pins, connected to brakes and lights are clearly not hot.

From the truck side, the #1 pin goes to the battery.  I believe it is only hot when the truck is running.  This pin, connected to the truck battery, will charge the TT battery while traveling.

If the #1 wire is shorted, then plugging the TT in will energize and fry the wire.

I suspect that you need to pull the truck plug out far enough to find the bare wire or shorted wire and replace that wire.
One reason it does not "smoke" when no TT is plugged in might be that the truck fuse feeding that #1 pin is removed or blown.

I hope this makes sense and helps.
 

Gary RV_Wizard

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The +12v terminal on the truck side may be either always hot or key-switched, depending on who wired it.  Powering that pin from an ignition-switched source prevents the trailer from sucking the juice from the truck battery while parked with engine off.

I'd start by verifying that the trailer wiring is still ok - something may have been damaged since the last time you used it. That pin on the trailer side should be hot, i.e. connected to the trailer battery. If by chance it has shorted to ground, that would explain the problem.
 

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purple haze

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Jul 13, 2019
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8
Thanks for the response, guys. I'm pretty familiar with the wire orientation on the 7 pin plug. Here's the latest. The #1 pin on the truck side was hot regardless of key position. I know this, cuz both times I hooked up, I shut the engine off when I get the hitch onto the ball. That's how I always do it. I have to do a "routine" if you will so I don't forget stuff. Lol. So, now that #1 pin is dead. I've gone thru the fuse box and the power distribution box under the hood and can't find anything wrong. I completely disconnected the hot wire from the truck plug and hooked up the trailer this morning and went for a few mile drive to check things out. Lights, brakes,etc. all good. I've towed this trailer many, many times with the wifes Silverado. That was our only truck for a while. I checked the #1 pin on that truck yesterday and it's dead, key on, key off, engine on, doesn't matter. So that would explain why I could tow with it and not have any problems. Now, for another wrinkle. LOL. I have used my daughters GMC to tow this trailer with as well. Not for about 2 years since the last time. I checked the #1 pin on her truck yesterday and it's hot all the time. That leads me to believe that whatever is causing the problem happened in the last 2 years since I used the GMC last.
Now, if that #1 pin on my f250 is dead, then, that means the truck wont' be charging the trailer batteries while towing, right? What is the drawback on  that? It seems that has been the situation for quite a few trips towing with the Silverado and we haven't had any battery issues. I always charge up the batteries just before leaving on a trip and we dry camp most of the time, so whenever we run the genny that charges the batteries, right? I always have a 110v battery charger with me too.

And lastly, to Gary RV, I looked at the wiring diagrams that you posted and it seems like they are opposite of what I have. Like maybe the truck end and the  trailer end got switched up. Idk

I can't get a pic to post up, but, on my plug on the trailer end has the hot wire at the 11 oclock postition. I confirmed that with a test light also. I just looked at the diagram again that Gary RV posted and I looked at the diagram that came with the new plug that I bought yesterday for my truck, and, yes,  they are opposite.
 

grashley

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May 7, 2015
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You are correct, the battery charging feature is a convenience feature.  It is the best wire to lose out of the plug!!

Here is the wiring diagram I use, and it agrees with you.  I hesitate to ever challenge Gary, but...

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

purple haze

Member
Joined
Jul 13, 2019
Posts
8
grashley said:
You are correct, the battery charging feature is a convenience feature.  It is the best wire to lose out of the plug!!

Here is the wiring diagram I use, and it agrees with you.  I hesitate to ever challenge Gary, but...

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

Right on. I think I'm good to go. Just need some time......
 

sc4668

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Apr 18, 2017
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265
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Brooklyn, MI
Take an Ohm meter between the #1 pin and ground on the truck and I bet you have a direct short. Now start at the truck trailer plug and work your way to the fuse box. A wire has chaffed thru and touching the frame.
 
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