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hey guys. i jus received my rpm tach from summit racing....i recommend them they are really good and fast on shipping. anyway i already hooked up my 12v, my dash 12v, and my ground...but im not sure where to hook up the last wire to. i know its either to the gauge cluster or ignition coil but i cant figure out where to hook it up. any help here please?

Me and my friend hooked his up to his civic...im not sure whats its called, but we connected it to the wire that connects to the stock rpm gauge...it is recommended for an accurate reading. (its under the hood somewhere...to bad i dont know **** about a civic)