generaly you just bolt the tach to the dash where you can see it, but is not blocking your sight. so some where it looks good.
your red one (+12v) you need to find a power source, there is not one that goes directly into the back of the instrment pannel, that i can see, so use one from the stereo or something. try splicing it into the light blue/yellow wire there.
For the black (ground) splice the wire into the brown/white wire on the back of the instrment pannel.
the third wire you need to splice into the black wire that connects to pin 7, PLUG K in the junction box in the left foot well. That is the tacho out put from the ecu.
im not 100% sure about this. just been looking thru the workshop manual and thats what ive got. as always you do modifications at your own risk and i assume no responsibility for any damaged caused.
i have installed the red and the black wire, but i dont get a signal from the tacho output in the junction box