So, the car was idling a little bit rough when cold and I suspected it might be the glow plugs. I went to have a look at them today and found the red wire going to the plugs was corroded and the end of it the (second image) came away in my hand.
The little plastic housing it was in was quite melted (first image).
The ring-end connection/terminal that goes on to the "bolt" at the end of the wire was fine, so I cleaned everything up (first image is after the job was complete), and wrapped the cable through the ring-end and put a heat shrink sleeve over it and used a cable tie to hold it in place.
The car seemed to idle better when I started it up, so I assume the glow plugs are doing some little bit of work now, instead of just melting the plastic housing.

So, my assumption is that it will be OK for a while, and that the reason the wire broke was because of a little corrosion, and so then there was more current going through a smaller area of the wire, which heated that part of the wire more, melting the plastic, which might have opened it up more, leading to more corrosion, leading to more melting, etc.
The wire wasn't hot after I started the car. And all seems good.

So, do you guys think this will be OK as a long term solution?
Or would I be better off picking up a new harness as soon as possible?
Or just a matter of picking up a harness when I get around to it, maybe in a few months?
I'll keep a close eye on it anyway.
I do like the "MacGyver" solutions, but I also dislike them because they're a bit messy.

 

gijoe, What you have is not a long term solution. i would spend the little bit and get a new harness. Not sure if you could just get the connector and solder your own wire back on (just make sure to get to good copper before attempting to solder, which may lead back to needing a new harness since the wiring will be too short).

I would also recommend getting what is called "Raychem WCSF". This is heat shrink on steroids. I use it where I work to survive a nuclear reactor melting down (literally, I work at a power plant). The real benefit of this stuff is your problem was from water getting down to the wiring. The Raychem has a glue on the inside that if you heat it up to shrink it down, the glue melts and then seals the heat shrink to the connector, making a water tight seal. I will admit that for heat shrink it is expensive. But, for conditions like under the hood/bonnet of your car, I would trust nothing else. You will probably need 2 sizes. You will need some Raychem WCSF-070 to put on the harness to build up the size of the wire (run this right up to where it attached to the bolt/ring piece) and then you are going to have a piece of Raychem WCSF-200 that is going to cover part of the WCSF-070 and up to the flared part (where your finger tips are in the second picture). This will guarantee that you will not have this issue in the future.

 

The name "Thermo" is fitting so then!
Thanks,
This was my initial thought alright.
Something in the back of my head had briefly considered soldering it alright though, but for some reason I just thought this stuff was "too big" to solder, and that it just wouldn't hold with the heat that melted the plastic around it. I didn't look too much at that "bolt" to see how it was originally connected to the wire. Thought it might have been welded or some other fancy method. I just think of solder as only being good for little resistors and capacitors.
But yea, I think I'll keep my eye out for a replacement anyway, and if it screws up in the near future I might try this method.

 

Being in the U.S. w/no diesel experience, is this the part?

JD61165

 

Yea, that's definitely it alright. Thanks!
But it's unfortunately the same part number as a fanbelt for Peugeot, so eBay search results are flooded with fanbelts! lol
but it will definitely make it easier to find the right part..
Nice one.