You're thinking of 20-year-old vehicles. There is no one wire anymore. The Engine Computer knows engine speed. It sends a digital signal to the Body Computer which interprets that information, then sends its own digital signal to the instrument cluster which is a computer module in itself. The most common cause of a dead tachometer is a defective instrument cluster. If you had a wiring problem, a lot more stuff would be not working.
Thursday, February 16th, 2012 AT 9:29 AM