Electrics

hi all new member
have had my 83 gti parked up for the last 3 years indoors.had to take it out recently mother inlaws garage a certin amount of moisture seems to of got in and dash lights have started to act up aswell as mfa and mpg guage.when i turn on lights to low beam works fine but then go to high beam all go out bar one side light on drivers side rev counter seems to be acting up to.from reading info on this site everthing points to the fues box but it seems to be dry if there is moisture in it, would a blow heater do the job or would i have to remove it to get it dry.all so if moisture got up around the clocks would be affecting things.
please help :?

Probably corroded earths - check em all