What is this?!?!? and a tach question...

What tach are you using? On a basic tach you'll have power, ground, lighting and sender. Some will have a shift light wire as well. Red would got to power, black to ground and white to the lighting circuit. If you are looking for the dimmer circuit a test meter will find it fast by dropping the needle when the dash is dimmed. You can easily test all the wires to find one to tap into.

That's assuming I read your question right.I just went through this myself... kinda daunting.