how do i know what a resister looks like on my ford focus(1998)??? ?

when i brought my ford focus from a private seller i noticed that the numbers 1,2 and 3 dont work but only number 4 works on the switch that controls the speed of the air,i thought it would be a easy job,just changing the switch,i was wrong,now i realise its the resister,what does that look like and where is it???