speedometer signal help
 

97 model lt1 v8 instrument cluster.
i have had a speedo sensor hooked DIRECTLY to the back of the speedometer and works great.
im changing my setup and need an adapter.
my old setup was a 4000 (4 pulse) AC sine wave signal.
trying to order an electronic adapter and im being told that i need a square wave signal.

the AC sine wave ive been using is a 2 wire setup.
the square wave setup is a 3 wire setup.
can a fellow third gen guy help me out?
the guy im ordering my parts from said my speedometer shouldnt even work since it doesnt have a proper power, ground and signal connection.
what do i order?