[dynamo]

Ive tried searching up how to wire in a tachometer gauge and cant figure out how to do it, I can figure out how to power the gauge but dont know how to get an actual reading for the engine RPM to the gauge. I was wondering if there was a wire or something under the dash I could splice the signal wire for the gauge into.

[The Gonz]

In my '83 Commodore it was as easy as tapping the low side of the ignition coil.
I suspect on newer cars, you're better off looking for an appropriate digital reading out of the ECU.
... but I'd be happy to be corrected.

[dynamo]

Well my plan was to find a wire that would have the signal for the tacho gauge but i have no clue how to find that wire and the ignition coil method isnt an option for me as i have 4 separate ignition coils for each cylinder and im not quite sure that would work as ive seen nothing about it on the internet

[The Gonz]

Does your tacho have a 4,6,8 switch? I think setting it to 4 and attaching the tacho line to the negative of any one coil will still work. In the service manual for the FD, pin 86 of the ECM terminal module carries the engine speed signal (tacho). Chances are the PD will have similar.

Here's your answer - pin 63:
Hyundai i-30 - Engine Control Module (ECM) - Engine Control System