tachometer 12v switched power(which wire????)

Hey guys, im new here, anyway ive searched and i know this topic has been covered... www.JDMfan.com is no longer a website.. i put the green to the blue wire with the silver dots on the back of the guage cluster... Attatched the ground, now the red power wire.. what do i use for a power source? i hooked the red to a random red wire on the back of the cluster wiring harness but apparently thats not working out..
So, what did everyone use for the 12v switched power wire?
PLEASE HELP ASAP, i need my car in 2 hours

anyoneeeeeeeeee

For me, I tapped the +12v power wire to a blank un-used terminal on the under dash fuse block, that's "hot" when the ignition is on.