adding an auxilary rev counter and shift light

[evo4terror]

hi does anyone now where the best place to wire in an auxilary rev gauge would be. i was going to connect the live, earth and switch live into the back of the stereo wiring as then will only work when ignition is turned on. the problem i am having is finding where to wire in the coil wire to get a rev reading. i have all the functions wortking on the auxilary gauge just no rev reading. i have taken out the normal dials in my evo 4 and cant find any wiring in the two wiring blokes that make the rev counter work.

will post pics of this dilemna soon