1991 saab 900 turbo automatic 105k. When I drive over 3200 rpm on the tachometer, the charging idiot light comes on and then goes back off when I slow down. I had changed the brushes and voltage regulator about 6 months ago. What is the most likely problem with this charging failure at higher rpm - is it voltage regulator, brushes, alternator,belts, connection or something else? Thanks