interesting hook-up

OK, so maybe i misstated a bit, but anyways, heres the question:

I want to install a tachometer on my 95 corolla (actually a geo prizm...but lets not get technical) so im going to go to a junk yard and grab a whole new guage panel/cluster, spedomemeter, gas, temp etc. and install it.

Before I do this, Im looking for help as to how to know weather or not my car already has the hook-ups. I checked for thr requisite green wire on the ignition coil, and it appears to go to the speedometer cluster. But is there something tell tale i can check for, b/c right now, after I have removed the instrumentation panel, I can't just look and say, 'oh, there's the hook up!'.
Would it normally be the case that if the car DOESN'T come with a tach, that the hook-up to the coil would have to be done?? Or is it possible that the leads already in place on some makes/models??

Help here appreciated. Thanks.

Omar

most OBD2 cars come prewired for any gauge cluster to save cost and because the ECU needs that information to run. your car is OBD1 though so I'm not sure.

hmmm......

inconclusive, but thanks for help.

Omar