Heater (blower) stays on

I'm pretty sure this is a heater switch resistor issue. Can someone tell me where to find the resistor so I can replace it? Also, my best option for a new resistor - new (expensive?) or used (worth the risk?).

1983 633 csi

Thanks!

http://home.normgrills.net/bcg/Heat_%26_AC_FAQ.html#anchor1090602

Later,