Did you check the main Ground connection from the battery to chassis and the distribution box for the smaller + leads that feed all the auxilliaries that is mounted on the engine side of the firewall in front of the battery?
I agree with Brian, this is not an alternator problem.

__________________
1991 M-B 560SEL Arctic White/Grey 99,000 Miles
1987 M-B 300SDL Ivory/Palomino 229,000 Miles (sold but never forgotten)
2006 Volvo XC70 Blue/Beige
1999 Porsche Boxster Arena Red/Savanna Beige
1986 Porsche 928S Goldweiss/Brown