You could do the sensor mod by removing the photo cell and inserting a resistor to fool it into thinking its always daytime. I'm not sure on what value of resistor you need, but considering its GM and the *-10'* are GM, on the S10 forum, they use 2 different resistors depending on the year. 99+ its a 2.2K ohm 1/2 watt resistor. This can be found at Radio Shack.
Otherwise, I think you may have a Body Control Module problem.