So I went out this morning and my 1995 300tdi defender is dead. It starts perfectly but as soon as I let the key go it cuts out. If I hold the key in the start position it runs fine and drives fine. It was working perfectly yesterday so I am Abit stumped as to what went wrong. If anyone can help I would appreciate it.

 

the last defender post sounded very similar to your issue and it ended up being the ignition switch. do you have a meter or test light to test the switch in the column? at the moment I only have the gas d90 wiring diagrams on this computer, the brown wire is the battery feed to the switch, white with red the signal to the starter relay, white with orange aux power, and white is ignition power. if your losing one of the last two the ignition switch could be the cause.

 

That was my first thought as well but it was not the problem. I couldn't get my head around it so I had to bring it to the vet and thanks for the help