i decided to re-install my 5 inch tach after a few mos, but i forgot how to install it,
so here's my Q, i tried somthing new and it works, but i dont know if it may be dangerous.. for the power wire, i took out the ignition fuse and put the wire in and forced the fuse back in..

 

it would be wiser just to tap into the 12v wire with either solder or a t-tap.