1985 chevy scottsdale Electrical problem CAN SOME ONE HELP

Well I have try for some time now to find the problem and well i am out of ideas. Like i said i have a 1985 scottsdale 3/4 ton truck I bought it from a guy who overhauld the engine well first their is the problem of the tachometer none of the gages inside work the oil, battery, rpms, odometer, temp etc none work the signal lights work so do the head lights. I have looked at the distributer and found out that the tach wire was not plug in but when i put a new connection on nothing happend. There is also one more problem on the  fuse box the number 20a fuse on the GE/Idle box well it keep burning i have tried to look back at the wire see if the are shaffing or cut nothing. Can some one help me.