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I've got some time now that school's out so I'm going to try this, but I need a little help.
I've been wanting to build a set of sequential LEDs that run up with the engine RPMs like on an F1 steering wheel... its a line of LEDs that progress from green to yellow to red as the engine revs up... I'm pretty sure I can do it since I have a feeling the voltage to the tachometer varies with RPM, and thats what moves the needle... now, which wire is it? If I can figure out the right combo of resistors, then this will work and I'll have LEDs going off at 4000, 4500, 5000, 5500 (green), 6000, 6500 (yellow) 6600, 6700 and 6800 (red)... then mount it on top of the gauge cluster so I don't have to look down and obviously put a switch on it so I don't have to look at it all the time. So I need either the wire in the computer or the one to the cluster... either one should do the job. I'll bust out my multi-meter and V=IR and plug some of this crap out....
I searched tach wires and too many different things are listed... someone gimme what the tech manual says. Thanks.

 
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7thgencivic has a wire guide for 2001-03 and it says that the color for the tach is blue. you should go check it out.

 
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I'm actually going to take a guess that the tach output from the engine computer is pulse-width modulated and not voltage amplitude modulated. Much easier for digital circuits to deal with the first. If you've got an oscilloscope handy, that would help you a lot in figuring out what the engine computer is sending.