i've recently lost the last speed setting that was working on the 1979 heater fan switch ...... i was told its just a few resistors that need replacing . Any Help ?

 

look in haynes or fsm found here. there's only one i know of and thats on the backside of the blower motor housing.(under glove box) it only has 3 bolts holding it in. i have to change mine too. didnt work at all so i hard wired a switch to it and the batt.