Mystery fried wire(s)

Can anyone tell me what this wire (or these wires) connect to? I have a 2003 SR5 MT 4x4 3.4l.

When I was exploring routing wire for a future kill switch, I came across a fried wire. I have not been able to find any fixture that doesn't work - which could be worse if there's still current passing through this wire.

The first photo shows where the wire bundle is located. The second photo shows the burned wire in the bundle that passes under the carpeting below the driver's seat. I believe it is brown (BN). The insulation is not melted from the melt point forward.

The bundle then passes into a white plastic casing that I am guessing is a junction box. The wires appear to take a right turn through this box. (It's hard to tell without taking out the seat which I know I will eventually have to do.) As the (new?) bundle runs from under the seat towards the rear, I can see what appears to be another fried wire but I think the insulation is green. (Photo 3)

I am the third owner of this truck. I have owned it for 12 years and never smelled a short. The only electrical mod I've done is to install an isolated dual-battery setup to charge my camper battery while driving. None of the affected wires are part of that system. https://expeditionportal.com/forum/...eap-isolated-dual-battery-setup-for-50.77503/

Since I currently can't tell the origins of the wires, wiring diagrams are of limited help to me (as a novice), especially since the diagrams I can find don't show the routing.

I'm also curious how a wire gets fried like this when fuses are supposed to protect wires.

Thanks for any help you can provide!

 

BN that runs through connector BN7 would be the supplied ground for the fuel pump and the sending unit.

 

Thanks for finding this. I’m surprised those units are still functioning. I need to take the seat out and get a better look. Hopefully, I can just shore up the insulation on the ground wire with liquid-applied insulation but I need to figure out the second badly fried wire as I assume that’s where the short occurred.

I assume all these circuits are fused so I’m wondering how the wire burned up without the fuse protecting it.

I did discover that the passenger seat belt alert and one license plate light aren’t working but I haven’t tested those circuits yet.

 

UPDATE: I removed the driver seat so I can see the junction up close. The green I thought was the wire color of the back fried wire was instead oxidation on the exposed conductors so I'm dealing with only one, not two circuits.

The damage to the in-going brown wire and the out-going brown wire appears to be isolated to about 4" on either side of the junction. I can see no visible reason for the short.

1. Am I correct to assume that the cause of the short is the junction?

2. Can I repair this by bypassing the junction? I would cut out the bad sections on either side of the junction and directly connect the two good sections with an added section of wire. I don't have to turn the wire at right angles.

3. If my idea is bad for some reason, does the whole junction box need to be replaced?

4. If the junction box needs to be replaced, or even if just the fried wires need to be replaced (how would I know if the problem is in the junction box or on the wire terminals?), how are the individual wires released? Are the slots adjacent to the wire inlets release points? (Photo 2) If so, are specialized tools needed? The outlets (Photo 3) are different; there are no adjacent slots. How are the wires on that side of the connector released? I separated the two halves but the interior is so packed with dielectric grease, I can't see anything.

4. If I do need to replace the terminals on the brown wires and work through the existing junction box, it appears the terminals are not spades, but rather "barrels." Are these a type of terminal that can be crimped or soldered?

5. Why wasn't a fuse tripped? And why has this wire not continued to overheat and deteriorate further?

 

Definitely something screwy going on there, there should be no current on that wire as all it grounds is the sending unit for the fuel gauge. I'm wondering if someone didn't tap something into it somewhere between there and the fuel tank.

You can cut the bad section out and just bypass the connector with a length of wire but you need to determine what is causing it to carry current.

 

I’m relieved to learn that the wire is connected to the sender, not the fuel pump. Losing the gas gauge is a whole lot worrisome than having the fuel pump go out unexpectedly.

Sorry if I gave the impression I had tested for current. I did not…or can it be assumed it was carrying (excessive) current since it shorted out? Obviously, I am not well educated when it comes to automotive wiring.

I did trace the wire harness all the way back to the fuel pump area to look for any visible issues and I did not see any wires coming out of the loom to indicate somebody had tapped into the circuit. Nor did I see any wire tap under the dash. Tomorrow, I’ll check the wire going forward into the engine bay.

Perhaps I should wire in an inline fuse to prevent another melt down.

 

I mean it's apparent that wire is having or has had excessive current passed through it.

The only other logical explanation is it is shorted to another wire in the harness.
You may want to check all the fuses and make sure that they are all the correct rating and someone hasn't put a higher rated fuse in somewhere.

That would definitely be a good idea until the root cause is found.

 

I can only guess what ever caused this problem happened before you bought the truck.

The issue was corrected the circuit protection replaced since it did not open again no further troubling shooting was ever done. Then the last owner may just have not bothered to replace the melted wiring.

Depends on your nose I would have smelled that for a long time the smell just became back ground .

The possibility does exist that other adjacent wires may have melted but have not made contact as of yet.

Good luck!

 

Something had to have been seriously out of whack or mis-wired to melt a sensor ground like that, I wonder if there's any other melted wires elsewhere.

 

Amazingly, there was very little melt into the adjacent wires’ insulation. None of it looks deep enough to threaten exposing other conductors.

 

For anyone with access to the full wiring diagram, which fuse is this circuit supposedly protected by? Or would the fuse only protect the positive wire?

Could this be the cause?…

I have a pop-top slide-in camper. I installed an engine battery to house battery connection for charging while driving. I used an add-a-fuse doohickey to add a 7.5 amp fuse for the isolator into the 7.5 amp ignition fuse slot. There are also right-sized fuses on both the positive and negative cables between the batteries. Two summers ago, the house battery bounced up onto the metal casing of the battery box (I have since added a tie-down) and shorted out, frying a wire that ran to some corroded travel lights on the camper that never worked. I ‘m assuming the short found the path of least resistance to the damaged light wire. I don’t understand why the internal fuses didn’t protect that circuit, either. (I probably have some of the technical lingo incorrect.)

Is there any way these could be related? I don’t think I remember smelling any burnt wires in the cab though I definitely did in the camper.

 

It's a ground, grounds typically aren't protected by a fuse.
Most power wires that could potentially short to ground are protected by a fuse but if someone installs a higher current fuse than is specified and the wire protected by that fuse shorts to something it could potentially melt wires instead of blowing the fuse.

It's possible, electricity can take strange paths at times that one wouldn't think it would.
I think I would repair that wire and put a 5 amp fuse inline to be safe, if the fuse blows you know there's a fault still present somewhere.

 

Doubtful we will every know the cause .

Electric will tend to take the easiest path.

As simple as system voltage contacting any place in that Ground circuit including the Air Bag Module and the Combination meter .

A aftermarket install done wrong That has been removed .

A high current draw load using that ground point .

The interesting and strange wiring I have encountered over the years.

 

Well, after I removed more tape from around the wiring bundle, I discovered the melt damage on the ground wire appears to extend the length of the wire, at least from the junction box to as far as I can see under the dash. There are points I can see where bare wire is exposed. Without opening up the loom underneath the truck, I can't see the condition of the wire from the junction box to the fuel sender but I have to believe it's damaged the length, too.

It seems a massive (and very expensive) task to expose this wire the length of it's run. Ignorance was bliss. Who knows how long ago the short happened yet the circuit has continued to work. Since the wire is just a ground wire and thus shouldn't - normally - have much voltage running through it, I have two questions:

1. IF (and I recognize it's a bad idea to guess) the short was a one-time incident, what risk is there to just leaving it more or less alone - only adding some liquid insulation to the points I can easily see are exposed?

2. Why does the ground have to return back to a group ground at the front of the truck? Could the fuel sender be grounded on the chassis near the fuel pump instead?

 

I don't see why not, the gauge may not be quite as accurate but it should still work.

 

#2 It comes down to how the trucks are built on the line. How the wiring harness is made .

It should work just fine after making sure you have a good ground at that location

What I have done over the years is run another ground from the battery to the frame . Making the frame a Good ground in the rear of the vehicle,

Good Luck!

Trailer lights and brakes worked much better.

 

Sounds like its time to pull the seats and carpet back and do some rewiring. It sucks, but it shouldn't be too bad. The ID ground is in the driver's side foot well. Like some others have said, put a temporary inline fuse there to be safe. You could put it right next to the ID ground for easy access, in the case it does blow or you want to remove it.

 

Honestly, it's a ground wire. All the insulation got burnt off of it because a high amperage electrical current was sent down that wire. It still works because it can basically ground anywhere that it is exposed to the body ground. I wouldn't bother pulling the wire out of the harness, just find the stock ground point and run a new wire along side. Just abandon the original wire in place, just disconnect the ends. You should trace the wire and try to find the extent of the damage so you know what should be replaced, but it's not worth the effort to remove it.

 

I totally agree with running a new wire from the ground point IG with added fuse. I got all the parts and hope to do the replacement today. I'm wondering, though, if in order for the fuel gauge to work correctly, the new wire has to go through the three relays shown in the diagram below.

My wiring diagram source (Auto Repair Source online through the library) doesn't seem to list the cross reference codes so I can't find more details on the electrical components like location. It would seem common sense that Junction Block 3 which houses the three relays (if I'm interpreting the diagram correctly) is physically between Connector BN7 (under the seat) and IG ground which most likely puts it in the foot well. For anyone with a better resource, is that correct? That area is jam-packed with wiring harnesses and J/Bs.

And where does the ground wire for the relay at the top of the block (off pin 17) go to so I can look for damage there?

I appreciate the tip that the ID ground is in the driver's side foot well. The wiring diagram gives a bit more specificity in saying it's located around the left edge of the "reinforcement." What is the "reinforcement?" I ask because there's another ground on the right edge of the reinforcement.

I really appreciate all the suggestion thus far!!