mr z28

Went an bought a msd tach adpter an still cant get it to work. could someone tell me if I pull the cluster out how many wires to the tach I think its only 1 a white if I hook it to the msd box it still doesn't work. they is no filters in the line unless they are behind the cluster. when you turn the key on the tach will jump but when you start it it goes to zero. please help what can I do. Thanks.