I had a similar problem with my switch got another one and it did the same thing.
So i pulled one apart but you have to be cafeful when you do this as there are three springs inside as well as two plates and three bearings ( from memory ) and you need to make sure you put them back in sequence.
Video of the operation can help if you get lost.
When you are sure you are right with the sequence clean the brass plates rub with 400 wet and dry used wet to clean up any dags and then polish them. Also check if the plates are bent.
There are also a number of contacts on the back of the ignition switch which need to be cleaned as well.
Then the whole switch can do with a smear of light grease, the hard part is getting it back togeather properly. You can see the little clips that hold it togeather, be cafeful with these as they can break easy.
The problem is that contacts on the back are touching when they should not be causing some of the electrics to activate.