altenator/charging system/rear defroster

Hi guys,i was having a problem with my 05 impala with lights dimming with the heater,lights and rear defrog on and when i hit the gas it would brighten up,battery tested fine and always starts,i shampoo my engine a lot and a mechanic told me my altenator ma be corroded inside from all the washing with water and to spray the altenator down inside with wd 40 and said there may be some corrosion on the wires inside it,i sprayed her down and after a day or so my charging is fine and with the heater on and rear deforst she seems not to die down as much as before,has anyone else out there did this with thier altenator

I've always found that the lights dim and the heater slows down when you turn the rear window defroster on since I bought the car. always assumed that the defroster Just draws a big load, and the alternator doesn't produce as much juice when your idling at 750rpm.

I've always found that the lights dim and the heater slows down when you turn the rear window defroster on since I bought the car. always assumed that the defroster Just draws a big load, and the alternator doesn't produce as much juice when your idling at 750rpm.Yes you are correct but at the time my heater used to slow down like it was on the half or less ,my dash lights dimmed and my headlights,but everthing is better now what ever happened since i sprayed wd-40 into the altenator,how ever yes the heater slows a little because rear defog's do drain a lot of juice