can't get to tach to work right

[novafrog]

using a Dakota digital sgi-8d called d-d one guy said set cylinder count to 4, one said set it at 8 ,said to set switches 1 and 3 on 2 and 4 off and use output2 did both ways didn't work getting about 300 rpm's a idle I get 300 rpms when i take white wire coming from comp.and hook it to tach wire,trying to hook 2000 5.3 to factory tach in 72