When I purchased my car I discovered it had blown this 80 amp glow plug fuse , on further investigation I found the cause to be the solid metal strip that connects positive power to the glow plugs was bent and shorting to the engine block , I bent it out of the way and made sure there was plenty of clearance , replaced the 80 amp fuse and it has been fine ever since.
To change the 80 amp fuse you need to actually undo/remove the whole fuse box to get underneath the 80 amp fuse as it's bolted in place and can't just be pulled out like a normal fuse , you need to undo the bolt at the bottom of the fuse and it will come out , just do the opposite to install the new one.