I have been trying to install a tach instrument gauge in my truck for sometime now. I have tried two different ones that I got from a pick and pull and the tachs would not work. Thinking that maybe the gauges were bad in those, my buddy let me try his working cluster out of his truck and it would not work.

So, I am thinking now that I have a wire issue somewhere from the coil the the gauge. I tried checking the resistence from the coil to the cluster connector and had none. So I started back at the coil and followed the wire back to the ECM connector. I disconnected the connector and checked the resistence from the coil to the ECM connector and it check out good. I tired checking resistence from the ECM pin #4 to the cluster connector and had none.

So my question is how can I check for a bad wire from the ECM to cluster connector?

BTW: all the other gauges work so I am getting power the the cluster. I am just not getting the readings from the coil to the cluster.

1987 F-150 302 C-6 4x4