had alternator rebuilt due to warning light coming on. it worked fine for two days then light started coming on again at idle. raised idle to 900 and it works fine.guy at shop said it was the underdrive pulley.does anyone else have this problem with an underdrive on. checked voltage and main wire from alternator and top small wire in harness(green) have 12 volts.but the bottem wire(white/black)only has 10 volts at idle(dont know if this matters)

 

U/d pulleys do affect alternators but it shouldn't cause that. Take a volt meter to the battery while the car is running. A rebuilt alt should not go out in 2 days!

 

the shop wants me to put the stock pulley on and bring it back to the shop so they can check it.the battery is a year old so im thinking its just a wire somewhere.

 

the shop wants me to put the stock pulley on and bring it back to the shop so they can check it.the battery is a year old so im thinking its just a wire somewhere.

 

Do you have a large stereo system or other electronics above the stock car? (including new headlights/fog lights) Underdriving the alternaotor, while raising the amp draw of the stock electrical system could cause a problem.

 

just a sony head unit

 

I think underdriving the alternator is only noticed under high electrical loads like I described. So I don't think the problem is at all related to underdriving the alternator.

 

Just curious, what alternator warning light? I didnt know the car had such a thing. Does it just tell you when it isnt producing power or what?

Also, how does it work? Where is the sensor?