[Forrest]

hey I have a 72 in dash tach, it has a two prong plug at the rear, it came out of a 72 gto with the unitized ignition, the other tachs pre 72 without unitized ign. have only one wire for the tach, when i hook it up ( the one wire to the neg. side of the coil) on my 70 gto it works but is reading about 500 rpms too high, I`m not sure what to do with the other wire (pos. or neg hook-up?), I have all the assembly manuals for 70`s and up but they all only show for the single wire tachs even the 72 books with schematics, what to do? please help, can i get this 72 tach that was for a untized distributor to work on a points type distributor? all the other tachs I`ve seen only have the one wire type tach? thanx