Ok, this is like pulling teeth. Any background info you can provide helps. Did it just crap out one day? Was it being quirky before it died (to try and narrow down whether the tach itself crapped out, or the wire). It seems to me that the signal wire comes from the puter itself.
What happen was my friend bought the car he yanked the motor, transmision, wiring harness, computer, pretty much everything.So I got a new motor, transmission, and put the wiring harness and computer back in the car. Everything is hooked up, and the only guages that work are the speedometer and the oil pressure guage. The temp guage didnt work, the battery volts dont work and the fuel guage dont work anymore. I have checked all the wires and they al look good to me.