So my Fiance has a 99 Sport 4.0 and when you turn the headlights on at idle the volt meter drops and belt starts to squeal for a min then stops and volt meter goes back to normal. While Driving there's no issue. This also happens when the heater/AC is turned on but worse if she turns the blower on and any of the vent settings. It will stay like this until its turned off . weather your at idle or driving. My thought was the blower motor going bad and pulling too many volts/amps, but im not sure and I dont want to replace if its not bad. I've replace the alternator, Battery, BOTH Battery cables, the belt seems tight enough. I've also replaced Power steering pump and water pump in the past. But this voltage drop and squealing is driving me nuts because I can't figure it out.

Thanks In Advance for any help

 

Sounds like the belt is slipping...either too loose or glazed.

 

+1. My belt was squeaking, but it looked new so I didn't think it was the problem. The boys here set me straight. A new Gatorback and all is well!

 

What he said.

 

This....I had the same problem...tightened the belt(I thought I had it tight but not enough I guess) and the problem went away.

 

Like most of these guys have said it sounds more like a tension problem. I had this problem before and I gave the adjustment bracket bolt a few more turns and low and behold the screech stoped.

 

I will try and tighten it a bit more today and see if it stops. The belt is a gator back about 5-6 yrs old so if that doesn't help I'll replace it. Thanks for the help