im having some problems with my alt ive had it tested and ive tried a new one and no change. i also have tried 3 different batteries and no change. when running my lights, my garmin, and radio at nite when im driving its charging about 14, when im at a light it drops to around 6, and as soon as i start going it jumps back up. i have tried changing the cable ends and same thing. i dont have underdrive pulleys. so im just at a loss

 

When your at a light and it drops voltage, then picks right back up when you start driving again, that tells me that your drawing power.. For your radio, is it a stock radio or do you have the whole setup with subwoofers and what not. The GPS shouldn't be affecting the voltage too much. My F250 did the same thing, I bought a new battery with higher CCA, voltage. It overall was bigger, but never had that problem again. For your radio, if it is the whole setup with the subwoofers, go with a capacitor.

 

Check the belt and or belt tensioner, sounds like its slipping.

 

its just a pioneer cd player with factory speakers, i have a 800cca battery. and i just checked the belt and its not slipping