Blower Motor only runs on high

[pugsy]

My blower motor only runs when the knob is set to high on the dash. It's a '92 xlt with A/C option. I've tried changing the relay under the hood as well as the knob switch in the dash and same thing. I've read posts that say that the resistor is what controls the settings - where exactely is the resistor on a 92? I've looked around around and see plugs, relay boxes for the blower motor but that's it.
Thanks!

 

[Jason94sport]

It's mounted directly to the right of the blower motor, on the heater box. It has 1 plug going into it.