2000 grand prix se 3.1 - replaced the fan blower resistor, worked for approx. 2 wks then went out again. also, when NOT working, if i turn to the fan switch to speeds 1-4 my headlights/daytime running lamps go out along with the fan not responding. to me, the untrained driver, it sounds like a serious issue. also, thanks so much for all the information AF users have provided so far.

So far based on your symptoms you may have a bad ignition switch and harness.