Taillight melted

[canyonslicker]

I'd be real weary of just replacing parts without checking everything out. The electronics in these trucks are highly integrated. A short in any number of BMS circuits could've caused it.

Usually a short circuit develops heat at that point and not from a peripheral module. But stranger things have happened. Who knows?

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[D Fresh]

Usually a short circuit develops heat at that point and not from a peripheral module. But stranger things have happened. Who knows?

And when that happens they often take other things out with them. And when those things aren't addressed they usually end up burning up the expensive parts you just replaced.

Granted the BMS is FET protected. But my years of experience troubleshooting TelCo equipment from a systems level to a component level tells me if you just replace the burnt shit, you'll be back to do it again.

Shotgunning a $1k + tailight assembly in the hopes it doesn't burn up again isn't very smart.

 

[canyonslicker]

And when that happens they often take other things out with them. And when those things aren't addressed they usually end up burning up the expensive parts you just replaced.

Granted the BMS is FET protected. But my years of experience troubleshooting TelCo equipment from a systems level to a component level tells me if you just replace the burnt shit, you'll be back to do it again.

Shotgunning a $1k + tailight assembly in the hopes it doesn't burn up again isn't very smart.

I agree, my experience as a tech and designer of RF and DOD equipment test systems.
Yeah but this seems more localized. It doesn’t hurt to do your due diligence just in case. My thought is an electrolytic capacitor decided to partially fail not causing a catastrophic shutdown in the BLIS taillight assembly. It’s all conjecture at this point. I’ve worked Telco systems in the past too.

 

[OFC Ranger]

Why I always run one way diodes when tapping factory systems.

Nothing is full proof, but that one step drops the probability a lot.

 

[maxbottomtime]

The taillight assemblies with blind spot are pricey. I’d expect replacement to be in the neighborhood of 2-3K. Who sold you the warranty? Could you not get an estimate elsewhere for free and then the warranty pays the shop to replace?
The assemblies are also vin locked so don’t think this is an easy DIY.

 

[D Fresh]

The taillight assemblies with blind spot are pricey. I’d expect replacement to be in the neighborhood of 2-3K. Who sold you the warranty? Could you not get an estimate elsewhere for free and then the warranty pays the shop to replace?
The assemblies are also vin locked so don’t think this is an easy DIY.

@airline tech has found that the BLISS modules can be programmed via ForScan. Changing the tailight and module should be rather strait forward.

 

[airline tech]

Ironically, I was just looking at this, but the wiring needs inspected for the whole system. Someone who is comfortable with meter, we only see evidence of the taillight assembly and harness.
There has clearly been a short circuit, bad enough to melt the harness, this could have led to a much worse outcome, I am talking total loss of truck.

Now, Only Assuming the short came from the BLIS, this is all the things on that specific power circuit that may/could be affected.

It needs to be investigated as what system shorted. Taillights, Turns, Back-Up or BLIS and dig deep into all wiring harnesses. to ensure integrity.
Just because it was generating a BLIS fault prior to this event, does not conclusively mean it was that system.
Now, the exterior lights are (Protected by the BCM) internally, so you would have had some messages related to that, so those systems could possibly be ruled out, but for safety they should be checked.

The main thing is how much wiring was damaged and how far forward did it go, and did it take out the other Left BLIS Module

It is possible to check the harness and identify the wires that have the insulation burnt off down to bare copper, there is most likely 2 wires down to bare. (Shorted Together) most likely from chaffing and Power Feed touching a Ground wire

Note: J = Fuse 23 in the BJB, it's only a 7.5 Amp Fuse, it should be blown

 

[Cactus Jack]

I just went through a very similar thing two weeks ago. My truck had less than 1,400 miles on it and one day on startup I got these four messages:
-blind spot system fault
-cross traffic system fault
-front camera fault
-pre-collision assist not available

Things that also stopped working:
-rear camera
-cruise control

I took it to the dealership and they said they had never seen four different modules stop working at the same time. Naturally, I was not very optimistic.
They had it for 2 days and finally traced it to a melted wiring harness at the driver’s side taillight. Luckily it only melted the wire and not the taillight like yours. They had my truck for about a week while the part came in and once they replaced the faulty wiring harness everything else was corrected. It was a very tense week though. In my head I was sure a bunch of other stuff got fried, but so far so good.

 

[fob63]

It appears to be internal to the taillight itself?
Melting onto the wiring harness.
I can't see all the connector pins from the photo but they don't look like they were a problem.
Fuses should have blown?
Do you live in a salty environment?

 

[Max Crafter]

i'm also wondering why fuses didnt blow first.
regardless, this is something Ford should be aware of, perhaps it will be the subject of a new recall if it turns out to be a design issue or faulty parts.

 

[Capt Jon]

My guess is something in the light assembly caused an excessive current draw creating heat enough to destroy itself. Usually the fuse will only blow when you have a direct short. It cannot measure current. You could get a direct short when the heat melts the wire jacket allowing the + and - wires to contact.

 

[TOMDEE]

Hello,

The past few weeks I have been getting an error about the blind spot monitoring system. If I would restart the truck the error would go away for some time, some times 100mi some times 5 min. Last weekend I was driving home and stopped for lunch. When I came out I saw my tail light bulging from the body of the truck. When I looked at it closer I saw that it had melted. I pulled it out and saw damage the the wiring harness and that quite a bit of the back of the tail light had melted and deformed.

Any idea what I should do? My ford warranty is expired. I have the MPP warranty, but I have a feeling it is worthless. The dealership wants $300 to look at the truck and file the warranty claim for me. Should I just file an insurance claim? Just replace the wiring harness and tail light myself? Something else?


I attached a photo of the wiring harness and tail light below.

THERE IS A TAILLIGHT HARNESS RECALL

 

[Trigganometry]

if the wiring for your brake lights is broken, that'll likely fall under the bumper-to-bumper warranty, or in your case the extended warranty. That there was a recall already for similar issues they probably wouldn’t give you a hard time doing warranty work on it. By the time it’s said and done the deductible will be happily paid! This one is probably going to run into 1000’s of dollars otherwise.

 

[ControlNode]

My guess is something in the light assembly caused an excessive current draw creating heat enough to destroy itself. Usually the fuse will only blow when you have a direct short. It cannot measure current. You could get a direct short when the heat melts the wire jacket allowing the + and - wires to contact.

While the fuse cannot measure current, it should blow when the current through it exceeds its rating. The problem is the wiring after the fuse may not be rated for the same current the fuse on the circuit is. Take for example a 20A fuse to 5 4A loads, the wiring to a single load on the circuit may only be rated for 5A (still 25% over the device's intended load) for its given gauge and length. But should that part malfunction in a way that it's drawing 15A, it will burn up the wire and still not blow the fuse.

 

[JimG_AZ]

Got the . It will be interesting to see what the 3rd party warranty company does. The dealer does not appear to be very confident on the warranty paying out since they want money up front. If the warranty company does cover this, are they going to fix it correctly or just replace the taillight and hope it gets through the warranty period.

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