1. A fault isolation detection circuit for detecting a fault condition in a multi-stack fuel cell system, said circuit comprising: a plurality of stack input stages each being responsive to a voltage signal from a stack in the fuel cell system; a positive stack input stage responsive to a voltage signal from a positive terminal of the multi-stack relative to reference ground; a negative stack input stage responsive to a voltage signal from a negative terminal of the multi-stack relative to reference ground; and a processor responsive to the voltage signals from the input stages, said processor storing percentages of voltages from each of the plurality of stacks that contribute to a voltage at the positive terminal of the multi-stack and the negative terminal of the multi-stack for a no-fault condition, said processor determining whether the fault condition exists by calculating the percentages of the voltage contributions of each stack for the positive and negative terminals and comparing the calculated voltage contributions to the actual voltages at the positive and negative terminals of the multi-stack.