Hello!

Bit of basckstory: So I usually work on my car (fiesta 1.0 2017, MK 7.5), but during the Christmas holidays the thermostat gasket gave up, the spare part would take 2 weeks to arrive, but my old mechanic could swap it in a couple days (which become a week and half but that's another story)

He told me he had to remove the ECU to reach the part, a radiator pipe somehow broke and changed it too, at a fair price tho (didn't make me pay the pipe)

Today while checking the fluid levels I take a look at the whole bay and... I discover this, a live wire from the negative of the battery, that probably went into some missing part that had to be placed on the battery frame.
As much as I work on my car, I don't remember at all what piece was there, if it's missing something or just if the cable has to be put under some washer somewhere near.

Can anybody kind point me out what is going on? Even just a photo of "how should it look" would already be of great help, as online I only find zoomed out photos...

Thanks in advance!!!

Is it the white and yellow stripe wire that is hanging?

Any evidence of a terminal where it used to be, has it come off the battery negative where the sensor is, (if it has one)?

Has your mechanic any spare bit left over or is it something he or she has done and will admit to?

If your sure it is a live wire and has come from battery negative it is almost certainly from the BMS.

Is this connected or missing ?

4 minutes ago, Shearers said:

Is it the white and yellow stripe wire that is hanging?

Any evidence of a terminal where it used to be, has it come off the battery negative where the sensor is, (if it has one)?

Has your mechanic any spare bit left over or is it something he or she has done and will admit to?

Yes it's that live wire there! I do not see any bit were it should be attached, also it's taped so close to the rest of the wires that I'm assuming the bit where it had to be attached must have been really near it. This is also why I hoped in some photos from users with the same car.

I'm pretty sure the mechanic messed with it (unintentionally) while removing the ECU (it's that metallic device with black pastic connectors, just behind the live wire in the photo) - he would never admit it tho and I would have to leave him the car for a week at least. So I wanted to solve it quickly by myself!

Just now, Theshed said:

If your sure it is a live wire and has come from battery negative it is almost certainly from the BMS.

Is this connected or missing ?

I made another photo, photoshopped-in the info lol
There also the other angle with my hand so is more clear

Tomorrow I may remove the induction pipe and check better on the ECU, the whole cable has also that plastic pin (beside my thumb in the second photo) to keep it from moving, which is detached from whatever rod it was pinned to :/

Of course the unasked question, are there any warning lights or something not working ?

1 minute ago, Theshed said:

Of course the unasked question, are there any warning lights or something not working ?

No everything is working fine and no errors are shown. Since the wire is yellow with green stripe, it's surely a ground wire, so everything works fine until suddenly something blows up

Looking better at it, it's (dirty) white with a purple stripe!

Sorry, thought you said it was a live wire.

Looking at your photo' from where the conduit branches off it doesn't look like it can go far.

Is there anything on or near the battery positive ?

The BMS goes from the little box on the negative terminal to the positive and the other to BCM

1 hour ago, Theshed said:

Sorry, thought you said it was a live wire.

Looking at your photo' from where the conduit branches off it doesn't look like it can go far.

Is there anything on or near the battery positive ?

The BMS goes from the little box on the negative terminal to the positive and the other to BCM

Ok so I gathered my memory from when I changed the battery last year, and I kinda remember that cable had to be pinned on the battery retention cage rod (it's also the only plausible attach point), the 2 cables inside the sheath are ore full purple, which I suppose is the one which goes down and then inside the BCM, and the other is the white purple-striped one, which I guess could only go on that sort of connector beside the positive terminal?
Just need to understand how to plug it in the connector 🤔

I made a very short video https://imgur.com/a/O3Afpuq sorry for the light but I'm using a magnetic lamp + headlamp since it's almost 21:00 here and very dark

PS: sorry I wrote live wire but meant just exposed wire

Video says not available. But yes the loom clip can only really go on the exposed bolt on the plate above the BCM.

The wire may well go to the BCM in someway, but they generally have large connectors direct to the BCM.

Either way it looks like you are going to have to make a repair to the wire at some point.

1 hour ago, Theshed said:

Video says not available. But yes the loom clip can only really go on the exposed bolt on the plate above the BCM.

The wire may well go to the BCM in someway, but they generally have large connectors direct to the BCM.

Either way it looks like you are going to have to make a repair to the wire at some point.

This connector here, I really hope it's not enclosed and can be opened to get the wire in, will try to work on it tomorrow evening, thanks for the help!

That looks like it. Shouldn't be too difficult to have a good look. Can't really see from picture but is it a pin on the end of the wire ?

If so it may just push in. Disconnect the terminal so you can see better.

On 2/2/2026 at 12:18 PM, Theshed said:

That looks like it. Shouldn't be too difficult to have a good look. Can't really see from picture but is it a pin on the end of the wire ?

If so it may just push in. Disconnect the terminal so you can see better.

I think I did it, the wire had no pins it was just bare copper, I disconnected the terminal and basically that connector is just a sealed capsule with a serviceable fuse, there's this tiny rubber gasket that traps the wire inside, I just pushed it in until it stopped.

I guess that's it, I checked with my obd scanner (mechanic didn't even erase the previous head thermal overload error code) and everything looks right, unless there is another way to check if the BMS is working properly, couldn't find anything on the web apart some guides on device batteries and error codes for electric cars...

Not sure how you would check. It measures battery condition.

I wonder could you check charging voltage with it connected and disconnected and see if there is a change ?