Read this:http://www.madelectrical.com/electricaltech/amp-gauges.shtml for an explanation of the MAD bypass mod (a highly beneficial mod), which is probably what was already done to your wiring harness which makes it difficult to replace. Undo the wires on the back of the ammeter (after disconnecting the positive battery cable) and then remove the old harness. Mod the new harness as explained in MAD and then install the new harness.