Or do you mean both your clusters worked ok when physically installed in your 99.5 car but not in your 04 car?Well, the cluster is good, both worked in the 99.5 and neither in the 04.
Pin 12 from the cluster should be the blue wire going to the alternator.Just did a continuity check on cluster to alternator wire - as expected no continuity. Didn't notice connection plugs shown, wonder if there are some. The wire at the alternator is a lot thicker than at the cluster.