1987 Ford Truck

Heater problem
1987 Ford Truck V8 Four Wheel Drive Automatic 112548 miles

my heater control switch only works on the lowest setting nomatter what setting you move it to. I replaced the blower motor, thinking maybe somthing was wrong with it from advise from a backyard mechanic. Could you please point me in the right direction on what to do next. Thanks for your time.
November 8, 2008.

Under the hood disconeect the heater motor connection. With a static light chec to see if there is a difernce in voltage when the switch it turned up or down. If no diference check the fan switch control under the dash.

Dec 16, 2008.