When trying to turn the fan on, the abs light turns on but fan does not

[ringo]

i have a 2000 3500 chevy van but figure it works the same as most other chevys since the fan controls are all the same. just had the head gaskets replaced and since then whenever i try to turn on the fan, the abs light turns on but the fan does not. just had the blower motor resistor assembly replaced and it worked for about a week then broke again. one exception though…if i turn the fan speed knob to off, then turn the fan directional knob all the way counter clockwise to off, then turn the fan speed knob to hi, then turn the directional knob to any one of the other selections, the fan turns on hi. but then if i try to turn it down to med or low speed, it shuts off again and the abs light turns on. please help, this is driving me crazy