So today, we recieved some snow in our area. I just got back from taking a short drive tonight, and I had to use a lot of the trucks normal features. I do have a sound system, and it was giving me problems, but after I lowered the bass, the problem seemed to stop, for that moment. So tonight, I had on my front windshield wipers, headlights, rear windshield wiper, and the heat on medium. I then had to turn on the rear defrost. After I turned on the rear defrost, I got to a red light. The voltage needle went down quite a bit, and everything dimmed. The rear defrost has a timer, and it shuts off after a certain amount of time. When the rear defrost finally shut off by itself, I was dropping off a friend, and he had the door open. While he was getting out, the rear defrost shut off, and I heard what sounded like a "click" or Popping noise. After the rear defrost shut off, and it sounded, the voltage went back to normal. I then drove, and when I got to another red light, the voltage was much higher than before. I then turned on the rear defrost at the light, and the needle went down again. It seems like the rear defrost is pulling a lot of power. I also noticed, that when I got home, I was parallel parking my truck on the street, I was in reverse, but I had stopped to see the tree on the sidewalk.So I was in reverse, stopped, with the wheel turned, and getting ready to back up, and saw that the needle was also low by just turning the wheel. Then out of nowhere, I heard that one time "click" sound, and immediately the voltage needle popped right back up to where it should be. It was like if the "click" sound caused the needle to go up.

 

i dont know too much about the electrical systems but as mentioned countless times, the voltage needle isnt an accurate reading. mine moves down when the blinker is on. every click of the blinker and the needle moves to the left a few degrees

 

It could very possible be the altinator..the "battery gauge" just shows what the altinator is doing..not how much charge the battery has. Also, when was the last time you replaced the battery? Could be an old battery..or one with out much charge...

 

I would have the battery load tested and check the alternator output. The alternator maintains the charge in the battery, but if the battery is weak (old) then the alternator will not work to it's maximum.
Cold weather will quickly kill a weak battery.

 

All that ^

Plus hte alternator puts out less power while the engine is idleing then at speed. So your "Stereo" could be the problem. Its sucking more juice then the alt cna produce. You may need a bigger alt, smaler pulley, or a better battery (more cold cranking amps), or all three?