Melted Tow Connector Wiring

[Tazbert]

Went to hook up my camper yesterday and the lights weren't working. Checked the connector, and it was dead. Looked under the back bumper and all the wiring insulation is burned/melted off and individual wires are burned through. Any idea what would cause this? The camper was still plugged into the house when I first hooked it to the Jeep - would that have sent a surge back up the line? Is that a no-no for an RV? This is our first RV, so we're still kind of clueless.

Any idea how big of a job it is to replace the wiring? We're booked for our first ever trip with our camper next Friday. Is this something the dealer should be able to fix quickly?

2021 Sport with Max Tow

Thanks in advance...

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[ShadowsPapa]

Went to hook up my camper yesterday and the lights weren't working. Checked the connector, and it was dead. Looked under the back bumper and all the wiring insulation is burned/melted off and individual wires are burned through. Any idea what would cause this? The camper was still plugged into the house when I first hooked it to the Jeep - would that have sent a surge back up the line? Is that a no-no for an RV? This is our first RV, so we're still kind of clueless.

Any idea how big of a job it is to replace the wiring? We're booked for our first ever trip with our camper next Friday. Is this something the dealer should be able to fix quickly?

2021 Sport with Max Tow

Thanks in advance...

I have never even tried to leave my campers connected to any other power source when hooking to any of my trucks. (sold last camper a few years ago, camperless now)

As far as I know, that harness is a long one. Every line in it is protected by a fuse in the PCD/fuse panel under the hood. Even the trailer lighting is on its own fuse for each function - trailer left brake, trailer right brake, and so on. Odd that it would damage wiring like that, especially more than one.
Having the camper plugged into the house should have had zero impact on the lights because the house power only takes care of inside lighting, appliances and so on. Been a few years but I'm not so sure some don't keep the battery charged when plugged in.
That being said - if everything were perfect, all that should have happened is impact to the 12 volts that goes to the camper battery. There should be no impact on trailer lighting (as far as brake, turn, tail, marker) as that's nothing to do with your 110 volt power. Those are isolated.
Are you sure it wasn't a case of the heat from a wire or two melting the insulation on the others because of proximity?
Also weird would be impact to the trailer brake circuit - that's distinct from all other circuits - it's connected to nothing else.

I've wired campers (rodents totally destroy camper wiring around here) and I've wired trucks to handle campers, including all involved wiring, and I just can't fathom something taking them all out other than the heat from 1 melting the insulation on others.

Fuse panel passenger side firewall under the hood, engine bay. Pull the cover and there's a "legend" of all fuses and relays in that fuse panel. Get your reading glasses on and check the fuses that handle trailer brakes, trailer turn and brake lights, trailer tail lights and so on and see how the fuses are.

 

[kevman65]

I have seen a short in the camper 112V system cause people to get shocked if they touched the tow vehicle. But I've never seen any type of back feed to the tow vehicle electrical system.
The camper's travel lights are a separate circuit than the camper 12V/112V circuit.

I would think all of your problems are just on the JT.

Do you still have tail/brake/turn signals on JT tail lights?

 

[Tazbert]

So, I got my multi-meter out and tested the cable. The camper is sending 13.7V 10+Amps back through the cable on the Aux circuit! I assume it's 10+Amps - my multi-meter maxes out at 10, and it was freaking out, with the probe leads getting warm within a few seconds.

I'm assuming no well-behaved camper should be doing this, correct?

 

[kevman65]

Something is cross connected somewhere. The camper will use tow vehicle power to charge the camper battery, but nothing should be coming back.

 

[Tazbert]

I've wired campers (rodents totally destroy camper wiring around here) and I've wired trucks to handle campers, including all involved wiring, and I just can't fathom something taking them all out other than the heat from 1 melting the insulation on others.

I think that's just it. The current was coming back on the Aux circuit, but it was high amperage. I'm sure that was quite enough to affect other wires in the bundle.

 

[ShadowsPapa]

Still confusing in a way. I believe the hot lead, the 12V lead from the truck is fused something like 35 amps...... I'd have to check but it's a hefty fuse.
Assuming there's a "short" in the camper wiring itself, it should have blown that fuse.
Let's say the camper is wired incorrectly, you could get 12v from the camper battery onto, say, the ground of the truck, causing melted truck wiring.

Here's one thing I have thought of:
The truck is factory wired. No chance for error. Wires are in harnesses, connectors, very accurate and in all of my trucks, all of the wiring I've come across, I've never seen or heard of one that was wrong.
That being said - this is the standard 7 position connector using slots (there's also one that uses pins and round holes)

Since the Aux 12v will be hot positive all of the time it will not matter if you have 12v coming from the camper. 12+ and 12+ cancel each other, no flow.
But what if someone messed up the camper wiring and is feeding the camper's 12v + battery connection to the wrong pin and it's on 1 which should be ground - you have full camper battery voltage hitting the truck's ground wire, melting it.

The reason I suggest it's a camper wiring problem is because campers are hand-wired, with whatever connector is needed at the time. Every single one I have owned, be it a car hauler, camper, flatbed, whatever, it was wired by hand, no ready-made factory harness. The end was put on by a person.

And what if the camper's ground and 12v aux were reversed?
Likely you'd blow the truck's fuse for that 12v aux, but the 12v feedback to the truck's ground, slot 1, would melt things.

My bet - camper wiring issues.

The truck's aux has 12volts positive. If everything is perfect, the camper's battery 12v+ is only going to be battery voltage to that aux truck connector, again, 12+ cancels the 12+ of the truck, there is no flow.
So the camper's battery can't "feed back" into the truck IF the trailer is wired correctly.

EDIT-
To make it easier, you can find all of the various connector types here along with the standards -

https://www.google.com/search?q=7+p...IZTABHYxCAmQQ9QF6BAgZEAE#imgrc=-jngmnHGPVpXPM

 

[Volksparts]

I think one of your positive wires is grounding out somewhere. Either a pinch in one of the wires, or part of the insulation is frayed and grounding out. I would test the positive wires with my multimeter with the other lead on the frame using the continuity tester. The one that beeps is your culprit. Trace that to your problem and fix it. Might be exactly at the point where it burned through. Wire could have been pinched there causing a burn in the insulation between the positive wire and the frame. My suspect since the truck itself didn't have an issue beforehand is that the trailer wiring had the issue.

 

[ShadowsPapa]

If the truck wiring were at fault, fuses would have blown.
I'll put my money on a trailer issue, either rodents or human error, etc.
If I put a screwdriver in that 12v aux slot and ground it, the fuse would go instantly after the spark.
The wiring I have seen (and fixed) in trailers is just plain scary. And the people that sell them are often wiring hacks who should have their tools impounded.

 

[Tazbert]

Thanks for the diagrams. Here's what I'm seeing when I take reading on the trailer plug, using the above diagram for a reference.

Any 2 pins, except for Pin 4 (Aux) - 0V

Pin4 (Aux) - Pin1 (Ground) - 13.7V
Pin4 (Aux) - Pin2 (Brakes) - 13.7V
Pin4 (Aux) - Pin 3 (Tail Lights) - 11.8 V
Pin4 (Aux) - Pin5 or Pin6 (Turn Lights) - 8.6V
Pin4 (Aux) - Pin 7 (Backup Lights) - 0V

I also got up under the jeep with better lighting and found that it was the ground wire in the harness that seemed to bear the brunt of the load. It melted its way out of the outer insulation as far back as I could trace it ('till it went above the spare), damaging other wires near it close to the connector.

 

[Jaxmax]

Check camper battery for correct connections Pos. and Neg.

 

[ShadowsPapa]

Thanks for the diagrams. Here's what I'm seeing when I take reading on the trailer plug, using the above diagram for a reference.

Any 2 pins, except for Pin 4 (Aux) - 0V

Pin4 (Aux) - Pin1 (Ground) - 13.7V
Pin4 (Aux) - Pin2 (Brakes) - 13.7V
Pin4 (Aux) - Pin 3 (Tail Lights) - 11.8 V
Pin4 (Aux) - Pin5 or Pin6 (Turn Lights) - 8.6V
Pin4 (Aux) - Pin 7 (Backup Lights) - 0V

I also got up under the jeep with better lighting and found that it was the ground wire in the harness that seemed to bear the brunt of the load. It melted its way out of the outer insulation as far back as I could trace it ('till it went above the spare), damaging other wires near it close to the connector.

Whatever you do, don't feed any voltage into any of the truck's connector slots! You don't want to have + voltage introduced into the lighting circuits. These won't appreciate that.
Not sure why you are using the AUX 12v + at all for anything as far as testing.

You should have 12 volts (12.6 tops) on the aux connector because it goes to the trailer's battery + terminal.
That should read 12.6-12.8 fully charged depending on the battery.
13.7 is telling me you have something connected to that trailer.
Make sure camper is not connected to the house or 110v
Make sure the camper is NOT connected to the truck.
before doing any testing.

You should have 12.6-12.8 volts at the aux (between aux at the trailer's plug and the trailer's ground)
Checking AUX to the brakes will try to engage the trailer brakes and of course, it's a ground point due to the low resistance of the coils in the electric brakes. So all you are doing there is saying there's a ground path. But since you likely have a volt meter between the AUX and trailer brake terminal, there's not enough power to engage the brakes, you are simply using the trailer brakes as a ground for the volt meter and measuring voltage at the aux terminal
As far as the lighting - all you are doing is connecting the trailer's battery + to each of those lights in turn.

Assuming a normal "12 volt" battery in that camper, we'll see what others say, but that's high. It's telling me something else is powering it up to that voltage. A camper not connected to the truck and not connected to the house (or garage) 110v should only read normal battery voltage of about 12.6 fully charged.
Does that camper have ONE battery? Just one, and it's 12 volts?

 

[Tazbert]

You should have 12 volts (12.6 tops) on the aux connector because it goes to the trailer's battery + terminal.
That should read 12.6-12.8 fully charged depending on the battery.
13.7 is telling me you have something connected to that trailer.
Make sure camper is not connected to the house or 110v
Make sure the camper is NOT connected to the truck.
before doing any testing.

This was with the camper plugged into shore power. I tried again with it disconnected and reading dropped to 12.6-12.7. Digging into the specs for the power distribution panel, it looks like it puts out 13.7V to charge the battery, when connected to AC. So this all makes sense now.

 

[Tazbert]

I think I know what happened. This was suggested from someone on a camper forum, where I also posted the situation:

"Could it be possible that when you were connecting the camper 7-Way cable to your tow vehicle 7-Way connector, that you accidentally reversed the connector upside down and tried to plug it in? The connector interface is polarized with a tab and cut-out such that it really can't be connected together upside down. But if you did this accidentally and applied some force, and somehow pins 1 and 4 physically touched upside down (even for a tiny moment of time), that could have caused the short circuit in the wires underneath your tow vehicle. In this case the current from the battery would flow from the battery to pin 4 and then back to the battery on pin 1, a short circuit."

This is just the kind of bone-headed thing that I would be possible of doing (just ask my wife!). I do remember fumbling around to get the connector plugged in, though I don't remember any sparks flying. But... this would certainly explain the damage that was done.

 

[ShadowsPapa]

I think I know what happened. This was suggested from someone on a camper forum, where I also posted the situation:

"Could it be possible that when you were connecting the camper 7-Way cable to your tow vehicle 7-Way connector, that you accidentally reversed the connector upside down and tried to plug it in? The connector interface is polarized with a tab and cut-out such that it really can't be connected together upside down. But if you did this accidentally and applied some force, and somehow pins 1 and 4 physically touched upside down (even for a tiny moment of time), that could have caused the short circuit in the wires underneath your tow vehicle. In this case the current from the battery would flow from the battery to pin 4 and then back to the battery on pin 1, a short circuit."

This is just the kind of bone-headed thing that I would be possible of doing (just ask my wife!). I do remember fumbling around to get the connector plugged in, though I don't remember any sparks flying. But... this would certainly explain the damage that was done.

That would take some serious trying as those connectors are recessed in the slots a bit, you'd have to tip and wiggle it, but it would send that trailer 12 volts to the truck ground, melting the truck ground wire. The truck's 12v aux would go to trailer ground but that would blow the truck's aux fuse.
That's the only thing that works, other than a mis-wired camper pigtail.
power and ground positions would be reversed if the connector was 180 off.
The other connections wouldn't be a big deal - lighting, usually without power to them.
One should never do anything at all, connect, check/test or otherwise with the camper plugged into external power. Always disconnect camper from any external power before connecting to tow vehicle.

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