'72 Factory AC - No 'hi speed' on fan

[ssuesens]

The heat/AC fan on my '72 C10 only blows low and medium. After searching this site, i found a couple threads that said to replace the relay under the glove box. I did that today ($19 from O'Reillys) and still no Hi speed on the fan. When I move the switch from Med to high, I do hear a click in the relay. I believe that the resistor controls fan speed on low & medium, and is bypassed completely for high speed. Not sure where to go from here.