I just bought a 90 f250 with a bad engine and an e4od. Got the engine in and it won't shift. Speedometer inoperable and tachometer was intermittent. Fiddled with the speedo and got it working, but tach is coming and going. Has a brand new ford tach sensor on it, and I've tried other sensor from trucks known to be working. What would I check from here? When the tach does work it shofts great.

 

i would check for a loose connection in the wires coming out of the sensor, at the firewall, and on the back of the dash.

 

Ok I straight wired it at the sensor, over where it plugs in by the passenger battery as well. How do I find which wire it is at the firewall?