Its a pretty easy fix by the sounds of it, id come and have a look for the price of a cuppa tea but your a little far away from me at the moment (until I move). If you cant be bothered im sure a garage wouldn't charge you too much just to do a circuit check on the electrics (some do it free) and then fix whats wrong. You can a clever gizmo that clips onto the battery terminals and tells you what is going on in the charging circuit.