I bought a lightly used digital 7 7530 ignition box. I got everything wired up and programed and my tach is not working. I used the gray wire which is the tach output according to the directions and get nothing. Upon further investigation the box doesn't have a gray wire coming out of it to the harness. The wiring harness that plugs in does but the one out of the box doesn't. Did msd make these boxes with no tach output wire? If so is there another way to get my tach to work without it? Thanks.