Melted Tow Connector Wiring

[JeffWithaJeep]

Not that I have any additional comments about what caused this, but my Gladiator had similar issue. I pull a jet ski trailer only. When I parked the trailer to put it up for off season, I know lights we’re working as I saw them working. When I went to hook up this spring, when I opened the cover for the 4 pin I also opened the cover for the seven pin. And out came a burnt broken metal tab and black powder. I looked at connector under the number and the entire plug was burnt up. So mine did it with nothing plugged in at some point since my last use. Dealer fixed as good faith, but only the connector was bad. No blown fuses or anything bad in the harness to the fuse box. I posted the issue on here a few months back but seems no one else had this issue until I saw this post.

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[Labswine]

Having your camper plugged into "shore power" shouldn't have caused an issue unless there was something wrong with your camper's wiring.

I connect to my truck all the time with my camper plugged into "shore power" with no issues...except that one time I pulled out and forgot to unplug from "shore power"...fortunately no damage to anything.

 

[ShadowsPapa]

Having your camper plugged into "shore power" shouldn't have caused an issue unless there was something wrong with your camper's wiring.

I connect to my truck all the time with my camper plugged into "shore power" with no issues...except that one time I pulled out and forgot to unplug from "shore power"...fortunately no damage to anything.

I partially disagree - surges, storms, there are things that can feed back into the truck.
If the land-based power is charging that battery at 13.7 and the truck is running and at a lower voltage, you are feeding back into the truck from the camper-based charging system.
I'm not sure I'd want that touching my trucks electronics.
I'll just say - I never have and never would have both connected. I don't want a faulty system feeding back into the truck. He had 13.7 from the camper - there are times the truck is less than that (mine has been at 13.0 and less when driving it)

I've been camping in the middle of Iowa popcorn storms and seen people leave with damaged camper electrical systems.

That's just me - call me paranoid, I don't care (I am) I just don't do it because I see no need or reason to, but can come up with logic to not.

LOL - I guess you came up with a great reason to not have both connected! If you have a habit of only ever connecting one or the other and never both - you can't drive away camper connected to the panel. ;-)

 

[ShadowsPapa]

Not that I have any additional comments about what caused this, but my Gladiator had similar issue. I pull a jet ski trailer only. When I parked the trailer to put it up for off season, I know lights we’re working as I saw them working. When I went to hook up this spring, when I opened the cover for the 4 pin I also opened the cover for the seven pin. And out came a burnt broken metal tab and black powder. I looked at connector under the number and the entire plug was burnt up. So mine did it with nothing plugged in at some point since my last use. Dealer fixed as good faith, but only the connector was bad. No blown fuses or anything bad in the harness to the fuse box. I posted the issue on here a few months back but seems no one else had this issue until I saw this post.

Tip - use a "no-ox" compound, similar to dielectric compound, in the connectors.
My guess is that a connection was either not real tight, or partially corroded. Bad connections cause heat. Heat leads to corrosion, breakdown of the protection on the terminals, rust, and a bad connection - see the circle? Heat = bad connection, resistance. Resistance causes heat.........
Once this started, it likely went quickly when not used.
They make simple greases or similar you put on electrical connections that prevent oxidation. They do not inhibit electrical conductivity. With a tight higher power connection like these you could use a dielectric grease without problems.
I've seen some connectors get really nasty, even eaten away in less than a year due to the "salts" used on the roads here - in under a year pins were half gone.

That was cool of that dealer to take care of that - of course who was to say there wasn't some sort of defect.......

 

[Tazbert]

We made it! Got my Gladiator back with wiring harness replaced on Thursday afternoon. Finally made it to our campsite around 10pm Friday. So much more prep work than I anticipated, and more trips to the hardware store. But.... our first ever trip with an RV (and our 35th anniversary) was a success! Thanks for all the help and advice from the group.

 

[dcmdon]

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?

is it doing this even when its not plugged in.

This is curious because even in this case, the fuses should blow before the wiring gets hot enough to melt insulation.

 

[ShadowsPapa]

is it doing this even when its not plugged in.

This is curious because even in this case, the fuses should blow before the wiring gets hot enough to melt insulation.

I believe it was resolved to be - the connector was tried up-side-down. That lined the camper's hot battery side with the truck's ground sending the camper's full battery voltage to the truck ground. Why only the truck wiring was impacted is interesting but if the gauge of the truck's ground was was a bit smaller than that of the camper's hot wire, it can make sense.
That's really the only way this could happen. Turn that round connector up-side-down and the camper hot contacts the truck connector ground, the truck connector 12v feed hits the camper's ground wire. Because it can't be actually plugged in that way, the connector would be tipped, and only one side made contact - camper hot to truck ground, melting the truck's ground wire and since they are bundled, taking the rest with it.
Been there before. All it takes is one wire to have a problem and the whole bundle goes. I've done countless re-wires and wiring repairs and it's just one wire that forces you to replace 4 or 6.
I'd bet on that camper's hot battery wire slot hitting the truck's ground tab. If he had tipped it the other way to try to get it connected, then the camper ground would have hit the truck's hot, blowing the fuse.

His testing also makes sense as he was using an ammeter, not a volt meter, and the ammeter is like connecting the two spots he was checking together directly - it's a shunt.

We made it! Got my Gladiator back with wiring harness replaced on Thursday afternoon. Finally made it to our campsite around 10pm Friday. So much more prep work than I anticipated, and more trips to the hardware store. But.... our first ever trip with an RV (and our 35th anniversary) was a success! Thanks for all the help and advice from the group.

So cute! Love that little face.

Glad it all worked out and you got to enjoy your rig, truck and all.
I guess this is also a public service reminder - make really sure to look at the tab and hole in the trailer connector............. I used a silver paint pen to mark the top of mine. Call me paranoid. I get in a hurry sometimes and it makes me think first. I've done enough wiring in my life - time to slow down LOL

 

[dcmdon]

I believe it was resolved to be - the connector was tried up-side-down. That lined the camper's hot battery side with the truck's ground sending the camper's full battery voltage to the truck ground.

This is interesting. I have no experience with the 7 pin connector other than pulling my dad's race car with his Ridgeline.

Everything heavy that I've towed has been a boat with reaction brakes and those always used the 4 pin connector.

 

[Tazbert]

is it doing this even when its not plugged in.

This is curious because even in this case, the fuses should blow before the wiring gets hot enough to melt insulation.

Nope, this was when it was plugged in.

 

[jsalbre]

Unless you file a chunk of the connector off there's no way you're getting any terminals to contact on a 7 way inserted upside down. Even if you did manage to get something to contact, it would only be the ground and trailer brake pins on the trailer side to the 12v and tail pins respectively on the tow vehicle side. This would at worst cause the tow vehicle 12v line to be shorted back to it's own ground (via the ball coupler and/or safety chains) and would pop the fuse for that line, though more likely given the poor ground contact that ball coupler or chains make you'd have resistance so high that nothing would happen at all, save for maybe the tiniest spark.

It was 99% likely a loose connection on the 12v charge/aux line at the tow vehicle's connector. It heated up, causing the resistance to go up, causing it to heat more, etc, etc, until the insulation melted.

There's no problem having the trailer plugged in to the tow vehicle and to shore power at the same time. Your factory converter (the charger in the trailer) isn't going to produce high enough amperage to damage the wiring in the tow vehicle unless you've taken the tow vehicle's battery out and hooked up some high-draw load there.

 

[ShadowsPapa]

Even if you did manage to get something to contact, it would only be the ground and trailer brake pins on the trailer side to the 12v and tail pins respectively on the tow vehicle side.

If you have the trailer connector exactly 180 off, the 12v of the trailer connector is lined up with the truck ground. 12v+ would line up where the ground should be.

It was 99% likely a loose connection on the 12v charge/aux line at the tow vehicle's connector. It heated up, causing the resistance to go up, causing it to heat more, etc, etc, until the insulation melted.

The heat would be at the connector. I've fixed enough melted connectors that happened due to corrosion on the terminals. It heats that part, causes rough corrosion. The wires themselves are fine back in the bundle. The terminals get really hot.
I do auto electric - restorations and repairs. The wires themselves don't get hot when there's a bad connection.

This is a common example - a high-current connection that oxidizes and builds resistance. It gets hot which causes more oxidation and more resistance. The connector shell melts into a blob - but the wire is fine (white wire)

Terminal shell melts because of the high resistance, the wire is always fine -

A bad connection wouldn't have melted the wires that far back.

 

[jsalbre]

If you have the trailer connector exactly 180 off, the 12v of the trailer connector is lined up with the truck ground. 12v+ would line up where the ground should be.

The heat would be at the connector. I've fixed enough melted connectors that happened due to corrosion on the terminals. It heats that part, causes rough corrosion. The wires themselves are fine back in the bundle. The terminals get really hot.
I do auto electric - restorations and repairs. The wires themselves don't get hot when there's a bad connection.

This is a common example - a high-current connection that oxidizes and builds resistance. It gets hot which causes more oxidation and more resistance. The connector shell melts into a blob - but the wire is fine (white wire)

Terminal shell melts because of the high resistance, the wire is always fine -

A bad connection wouldn't have melted the wires that far back.

The key on the 7 pin is directly above the 12v connector, so any attempt to insert it upside down would result in that pin being unable to reach any pins on the socket side. This is by design.

The shell usually melts, but I’ve had plenty of wires lose insulation from that too. With a high enough resistance connection the wire, connector shell, and insulation can and will smolder, or even catch fire. I’m not sure the OP mentioned exactly where it was burned, but I’d bet it was in close proximity to the connector.

 

[ShadowsPapa]

Auto electrician, maintenance electrician license in the 90s, electrician for PFG in the early 90s, trained automotive electrician, still doing wiring and restoration.
That's where I'm coming from.

OK, I dug through my cupboards and tubs of wiring harnesses to get pictures.
When there is a poor connection, the heat is generated AT that location, that connection, not in the wire leading to that connection. The OP says the wires under the truck melted. Not the connector.
Here's photographic proof of what happens with bad connections - note that only the shell melts and the connector itself is damaged, the wires are always fine - ALWAYS, they never burn or melt. I've done too many to keep track of, likely in the hundreds or better - from wiring trucks and cars for trailers, to full automotive re-wiring to everything in between, including engine swaps and more.

Here's examples of what a "bad connection" does - heat AT the connector only, never the wire (and this is true of your house wiring, too - why connections are in boxes but wire doesn't have to be - if water gets into the breaker panel and the bus bar corrodes where the breaker makes contact, that point will sizzle, get hotter than heck, but no wires will be damaged)

I dug through some of my tubs for examples, photographic evidence, because it seems no one believes an automotive electrician........

I have several more tubs of car and truck wiring harnesses and collections connectors, but hopefully found enough examples to explain what did and didn't happen here..........

This is where you find the heat if a trailer connector is corroded and you have a bad connection - the resistance generates heat - and causes oxidation and burning of the contact points, the heat melts the plastic shell - but wires will be ok. The resistance cuts flow through the wires so they don't get hot. The terminal connector is sort of like the filament of a light bulb - the resistance causes heat. Light bulbs get hot due to that resistance and yet the wires never melt.

Wow, look at that plastic shell - MELTED, and yet - the wires are fine, supple, the insulation is fine right up to the crimp. Why? Because the heat of a bad connection is concentrated AT that connection, not along the wire. It's where the resistance is - the connection's contact areas.
In these cases, windshield leaks let water drip down the inside of the firewall to the dimmer switch connection where the connection corroded, built resistance, and like electric flow through any resistor or resistance, even a light bulb, that connector got hot. Not the wire. Wire is fine.

And here is another example - and a good reason to move the dimmer switch off the floor! Shell melted, wires are FINE, still in fact reasonably supple. Wire good, shell melted.............

Well, gee, there's the problem - corrosion caused resistance, power flow through a resistance generated localized heat, melted the shell. Connector itself got hot - wire is fine. In fact, a person really could have cut that terminal off and crimped on a new one and been ok once the dimmer switch tabs were all cleaned up and some No-Ox applied.

Remember when fuse panels were on the floor up under the dash - and a windshield leak allowed water to get to the wiring? I've repaired, replaced, rebuilt, restored many fuse panels over the years - and it's always the same - corrosion, oxidation, caused resistance at the connector which led to heat which melted the shell. WIRES OK, shell melted, connector/terminal is toast.

I could give dozens of examples -
A bad connection - corrosion, oxidation = resistance. Current flow through a resistance generates heat AT that resistance, not up the wire, not somewhere else, but at that point of resistance. The wires will be fine because they are carrying a lighter load due to the resistance inline with the wires. It is akin to placing a wire-wound resistor in the line, cutting current flow down big-time, wires run cool but that resistor will glow.
In fact, that's how many cars controlled the HVAC blower speed - sending the power to the blower motor through a set of wire resistors. The resistors got hotter than heck, but the wiring was fine.
A poor connection like I've shown above is a resistor, a resistance. Wires stay cool, they won't melt, but the connector will get hot, maybe even melt the shell.
50 years have shown me this, perceptual reasoning, logic.

OK, can you insert the trailer connector incorrectly? Well, that depends! It depends on the shell.
I tried - and literally got momentary contact when trying to force the 12v power adapter I have into the back of my truck and watching a meter connected to the adapter. I wasn't totally successful - but didn't give up.
And with this adapter, I can show that if you did get it in, even for a moment, up-side-down, you'd connect the trailer's hot battery lead to the truck's GROUND wire! And you'd fry the truck's ground wire.
Assume this is your camper's connector - look where the + and - from the TRAILER are -

Now, flip that trailer connector 180 degrees ->

Suddenly your trailer's + battery lead is where the GROUND should be. If you do make contact, you now will be feeding 12+ volts from the camper (13+ if it's plugged into the house) to your truck's ground wire.
Can it be done? Well, it's not easy, but yes. And the OP isn't the first or only person to ever be successful at getting it done!
I found by checking various connectors I have that some aren't as rigid as others, some will flex a bit, and some have tabs that aren't well recessed into the shell, and the way things are oriented, if you do succeed at messing up, my testing showed the most likely scenario is - camper battery+ to your truck's ground, melting the truck's ground wire and any wires bundled tightly against it.

Want proof it can be done? LOL - took me less than 5 minutes to find other poor souls who found out what happens when you are connecting in your sleep - and of course, like here, there were arguments "it can't be done" countered by "wanna bet?!"

Hey, OP - does THIS look familiar???? LOL - can't be done? He dun it -

And this guy, like me, figured it out - melted truck wiring because the wires were reversed by the connector going in up-side-down ->

And to make the OP feel better about such a goof - here's another guy who got 'er done...........

Anyway, a poor connection will not melt the wires, they will make the connector itself hot and melt the shell, or at least get it really hot.
Wires melt from too much current, not from a resistance in a connection.
Poor connection = resistance. Resistance drops current flow in the circuit, the area of resistance is what will get hot.

And yes, it looks like although it's supposed to be not possible, or at least not likely, some RV folk have found out the hard way - if it don't go in really easy......... stop trying. It can be done.

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