Directly behind the glovebox - empty the box, push in the tabs at the back to release it to a full down position to improve access to the connectors and mounting screws.
you will find it in the heater box, also where the blower is. it is easy to remove.
You'll find the heater blower motor resistor in the heater/air conditioner compartment. This compartment is location underneath the dashboard. This is the part that allows the heater blower motor to change the fan's speed.
You can find a heater blower motor wiring diagram for a 1978 El Camino is the owner's manual. You can also find it at specific auto part stores.
Under the windshield wiper you will see a grill it is in there. Pretty tricky to get out. you don't want to make the same mistake I did my blower stopped working and I got a new one only to find out it was the resistor that had burned out.
it is right under the glove compartment
The heater blower motor will most likely be located under the dash by the heater core assmebly, but first you need to be sure that that's the problem, it could just be wiring to the blower motor. Shouldnt be too hard to replace, and should be simple to find,
The blower resistor is usually found attached to the A/C-heater box under the hood.
The blower motor resides above the passengers feet. You'll find an electrical connector and three screws. Drop it straight down towards the floor to remove it. Transfer the plastic blower fan to the new motor and reinstall. Be careful not to overtighten the nut for the plastic fan or you'll damage it.
At the firewall on the passenger side
You can find the heater wiring diagram for a 1989 Buick LeSabre in the vehicle's owner's manual. You can also obtain it from various auto part stores.
Remove the glovebox and heater fan motor is at back on right hand side it twists out clockwise.
replace the carbon canister