Ok as it stopped working then sort of started working again I would go down the road of a bad connection somewhere. Check the earth first, this can come loose or get corroded, then go through each wire and make sure none of them are broken, this is where a multimeter comes in handy, if you don't have one then borrow one or get one from ebay or some such for a few quid, you'll use it anyway for other things on the bike. Not much else I can think of it being to be honest, someone else might have an idea so keep checking back to see what they come up with.
Just a suggestion, it helps if you say "hello" in the new members section, folks then know your not a one hit wonder. Just sayin!