98 ford mustang problems?

My 98 mustang has a problem with the blower fan it used to only blow on the high setting and now it just very lightly blows air out on high but not much at all what's wrong with it

First off, the reason it only blows on high is because the blower motor resistor went bad. The high circuit doesn't run through the resistor, therefore still allows the blower motor to operate on that setting. If you run it on high constantly, its possible the blower motor is worn out and needs replacing. You should also have the resistor replaced too to make everything work properly again… Everything related to your problem that is.