Disco 2 Rear demister blowing fuses-wires ok

my td5 will instantly blow the 30a fuse upon switching it on,iv checked the wires going to the door and they seem ok.i plugged my multimeter where the fuse goes and it read 14v,i know the car has to be running for it to work but does it really pull all that?
Any suggestions as to what's causing the fuse to keep blowing?
Any help or advice is always appreciated

There are two reasons why a fuse will blow; age, but we're talking years here, not minutes! The usual reason is a short circuit somewhere in the wiring.
Disconnect the rear screen heater at the connectors on the screen, nowhere else, and try it again, if the fuse blows then it's in the wiring, if not, then it's in the heater.

Blew with both disconnected
Wiring then as you say.Just a case of finding where now

Has the rear door been off?
Reason I ask, I changed the hinges on my TD5 and didn't realise the wire had been trapped between the door and the hinge and the sheathing had chaffed away causing the fuse to blow when switched on.
Very easy to check if you have the door card off - the wire should be able to be pulled up and down with no resistance

Unplug the door mirrors too and see if it blows that way too( the plugs are beneath that plate inside on the door)

Bigeeeee is the winner as I'm moving the wires the one to the hinge side is solid,lo and behold it's had a replacement door and they've caught that wire! Bad lads lol
Thanks for all the suggestions.