Unfortunately there are no magic bullets when it comes to diagnosing this sort of thing because the same, or similar, symptoms can have a number of causes. If you look at the third link which Jon supplied you will find towards the end a part on diagnosing such problems and this, or similar, needs to be followed to properly diagnose the problem without replacing expensive bits and pieces unnecessarily.
That said, my first port of call given that you say the problem is worse when damp would be to inspect very carefully all the relevant wiring and connectors.
Sorry not to be able to give the answer you were hoping for.
