What he said, all the indicator lecky goes through the hazzard switch, if these are never used they jam up when sudeenly they are and cause all sorts of problems.
Easy, but FIDDLY to clean take apart the hazzard bit let it swim in parrafin/diesel or wd40, blow dry, then spray liberally with furniture polish containing silicone, or if you can get some beeswax fill the switch contact area with this best stuff ever, done right it will never give another rproblem.
tabetha