If both sets of gauges went dead (you said this was a twin, right?), the only thing they share in common would be the ground. The tachs for instance, would each be powered through a fuse on the motor the tach was reading. So 2 different fuses, 1 for each motor. Point being, the chances of both those fuses letting go at the same time would be pretty slim. The chances they share a ground that's let go, much more likely....