I had some fun diagnosing the dead tach in my Trooper. It turned out to be a misaligned needle spindle, but I went through the wiring before figuring that out.

I cut the wires going to the tach sensor in order to fit a socket in there to remove the sensor. There is a connector behind the fuel pump, but I couldn't fit the socket over it.

Side rant: why did Isuzu use those crappy slide-on connectors for the temp and oil pressure sensors? It's disconcerting seeing my oil pressure drop off as a cross-wind moves the connector around.