Pontiac Repair: 1998 pontiac grand prix heater fan problem, pontiac grand prix, heater fan

Question
QUESTION: my heater will only run on high speed and then it will turn it's self on and off and every time it comes on it will turn the headlights off.

ANSWER: look at the fan controll resister block located inside the blower duct housing see if it is shorted thats what controlls the fan speed

---------- FOLLOW-UP ----------

QUESTION: I replaced the resistor and still have the same problem. I also noticed that it will turn off the rear window defroster as well as the headlights.

Answer
i wanted you to see if it was shorted first but ok buy repalcing it you have now took that part from the equasion, didi the terminals look coroded or heated up? youll need to check the grounds to the fan and power supply leads to the fan resister itself, the next step is to check the blower fan speed switch for a short or a burnt connection, also check the power lead from point of pos battery referecne, the power on the windows, heater and rear defrost go through a fuse even seperate they all have fused power supplys and if you kick one on and it robs the other you have a short in that circut or a loose powr suuply to the feed