We dont get really cold weather like it does up in the northern part of the country, but it can get down to the 30's sometimes at night during the winter months. That being said, would it be a bad idea to install underdrive pulleys when its cold, considering a person would use their heat, plus having kind of a large stereo (2 12's), and having HID lighting? Underdrive pulleys are not good if you have alot of power draw, right?

 

it shouldn't make any difference, if anything the alternator will be a tad more efficient in the cold. also, your engine should be making a bit more power in the cold due to more dense air and this can offer a bit more torque on the alternator. if you're ok in warm weather you're ok in the cold. also, remember your heater is the only real difference in what you're running. the heat comes off the coolant system.