Dodgy revmeter

[RevBillyG]

So, I was driving along when suddenly my radio decided to jam and blow a fuse. This took out my clock and revmeter as well as making my windows work strangely.
I changed the blown fuse under the bonnet and it blew straight away. I took out the radio, took it apart and removed the CD, put it back in and all was fine for a couple of days.

Then the radio refused to come on. So I removed it completely. Now, every so often the revmeter jerks to zero and back up to normal again. Looks like a short somewhere yeah? Any ideas what to check first?