I was looking at the back of my 1948 Fleetmaster heater switch and there are two items; 1 is a fuse and I’m not sure of the other. Any ideas on what that is, it’s difficult to see in a mirror. My heater 3 position switch only works on high speed the other 2 don’t work.

That is the resistor that reduces the speed. You need new swich, they are not dificult to find.