91 Olds 98 blower stay on all the time.

Hello,
I have a 91 Olds 98 tour sedan. My problem is the heater blower motor stays on after the car is turned off.
At present I must unplug the blower motor under hood to keep the battery from running down. I know that the power is always on in wiring diagram. I'm thinking the (blower resister assembly) may be bad, The blower seams to have most of the regular fan speeds.
The thing is it's a eighty dollar item plus where is it located. It must be under the dash and I sure hate to blindly tear in to the dash. I have checked things on the fire wall under the hood
all seams right, I checked the relays under the hood on the fire wall by unplugging them one at a time, but the blower keeps on running.
Please were can I get info on under dash items locations. I bought a repair manual, the wiring diagram doesn't
tell me of the resistance unit location.

Please help
Larry

Replace the blower power module on top of evap case r/s of top of cowl under hood, very common problem.