Quick look at the wiring diagram i am not surprised the instruments will stop the engine. I guess if you lose the tacho you lose the engine, but I haven tried it. The speed sensor is a good shout, it's connected to nearly all the instruments and including the tacho, green wire, if that had a short, you would blow the instrument fuse. The oil pressure sensor is not directly to the oil gauge, it seems to go through the tacho, via a white and green wire WG, and then a while brown WN.