My 1999 Octavia Tdi blows the fuse for the ECU?

 

First happened on the motorway in the rain, the car just stopped. After a bit of searching discovered the faulty fuse, so replaced and problem solved. I put the blame on the rain, water in the electrics somewhere. This lasted a couple of days then blew again, replaced the fuse again though this time blew within minutes. Now fuse blows as soon as I switch on the ignition. It's not raining now. I know it must be a short somewhere but does anyone know of any obvious places where these cars suffer electrical shorts, is it common for the ECU to play up? Is there a relay in the circuit somewhere? Need a starting point before I start investigation. Any help would be appreciated.

 

 

A diagnostic scan for fault codes would be a sensible starting point. Is it the 50A Fuse 5 which is blowing?