I have a 1991 W 150 and today I turned on the heater and nothing happened. It has always worked go for me before. I checked the fuse and its good. The blower motor doesnt come on and when I switch it from defrost to vent I dont even hear the plenum doors moving. Anyone have any ideas?

 

Most likely the blower switch, they are prone to frying. The wire on the back of the fuse box is prone to frying also.