Another Tach Question..

[268RTs4me]

My tach quit the other day, yes was working excellent, I disconnected coil wire. and disconnected from back of coil, hook up hot wire from coil wire went inside and tach wire was hot with test light, showing me my wire from coil to tack is OK. Hooked back up, so unpluged what I call hot wire from coil and it was dead, should get hot when ign is switched. I have no current flowing from 12 volt source to tach.. followed wire and goes behind fuse block, is this wire hooked into fuse block some where, or does it have a fusably link somewhere? My problem should be no 12 volt power to coil, just trying to figure where 12 volt wire comes from on 74 RR B Body. Thanks