Tach Signal question, timing loop vs. dash plug

[skillzilla]

Does anyone know what type of signal is given to the tach from the Y/R wire at the dash plug? Or more specifically, if this is the same type of signal that you get at the timing loop on the ignition harness (behind the head)?

I checked in the FSM and it says voltage to the tach should increase as revs increase, so Im thinking that the Y/R wire signal is positive voltage, while the timing loop at the back of the head gives an intermittent ground signal. Could someone confirm this for me please? I am doing an SR swap in my RX7 and wired up the Y/R wire from the dash plug to the RX7 tach signal input but its not working right, so Im considering trying to get a signal directly from the loop (I am thinking the RX7 tach requires a ground signal).

TIA

[skillzilla]

TTT, anyone? I need tachage!!