Electrical problem, need help

I have and 1981 and am having a problem.  I keep blowing a 20 amp fuse for the Tach, Volt meter.  It starts when the battery light comes on and then my tach and volt meter go dead and the choke light comes on.  I have replaced the fuse several times and the problem still occurs.  It seems that after I replace the fuse and drive it a few miles it blows the fuse again.  I have even disconected the tach and that does not solve the problem. Can anybody help me out on this its driving me crazy.