Smoking wires

Hi all, I have a 300tdi on an 'm' plate that seems to have knackered itself. To cut a long story short, my son does night shifts, went to start her up on tuesday morning at 6am and thought he had a flat battery as would not turn over and lights very dim, he called out AA who told him battery was knackered, gave him a jump start and he got home. Later that day I started her up first time with seemingly no battery problems. He did not use the car again until wednesday night, started ok but same problem 6am thursday but this time he bump started it and got home. I went out and got a new battery and fitted it but could not try starting it as son was out with the key(doh!) but lights seemed ok. He went to start it that evening and said that he had a flat battery. So I had a look and whilst ignition was on and trying to turn engine I could hear a relay or solenoid clicking. Son then told me there was smoke coming from under the bonnet. It looks like there is a fuseable link that has melted as the wire was very hot and came away in my hand.
2 questions (if you are still with me);
do i need to replace the fuseable link with another fuseable link or can i wire in a fuse holder??
any ideas as to what has caused the short??
All help and suggestions welcome, cheers.

sounds like a bad earth to me

Thanks Nick, I will grovel around in the snow after my brekkie and check the earth leads.

Right, plan of action after speaking to someone more knowledgeable than myself.
Replace or join fusible link with a fuse holder and 60 or 80 amp fuse.
Also think i have found the source of the short. The yellow cable that links either the injectors or glow plugs has corroded and is showing bare cable that is rubbing against some metalwork; i am hoping that this is only source of shorting.

Right, back to the drawing board.Wired in 60amp fuse in place of fusible link and rewired the glow plug wire but blew fuse as soon as ignition switched on. Will have to get someone out to have a look as i feel i could spend a lot of time trying to sort it.

Ok, for anyone interested, I have managed to fix the wiring. The short was caused by a failing glow plug, so I spent all morning replacing all 4 glow plugs - pig of a job, fancy having to remove the air-con compressor, mad!!!!!!
I also had to replace the wire loom for the glow plugs. Also had to wire in a 120amp fuse(thanks Anglia Battery) between the battery and the glow plug relay, this is made up of 2 thin sheets of fusible metal in a sealed container, much easier than a new loom or wire fusible link.
All seems ok and it starts up perfectly.