Started today going to church. 89 Mustang stock alternator. Got in boost battery light came on. Gauge showed no charge then back to normal.Tonight put vent on trans side of vac line to c-4 to get shift better, it is better. Done same thing every time I got into boost then went to normal when out of boost. One time did not come back to normal went back into boost came out then went to normal.Battery light and gauge agree with each other.Belt is tight on alternator and is still serpentine type. Haven't a clue what to check Needs someone smarter than me Help.Thank You