[PDF] SWP 118031 Diesel Tachometer Installation Instructions 1. If the tachometer needle goes to zero when powered up, but does not respond when the engine is started, there is no signal to the green wire. Check to ensure that the green wire is hooked to the proper location for a valid signal. 2. If the tachometer needle doesn’t go to zero when powered up, the tachometer is not grounded properly or Tachometer Wiring — The Art of Diesel Because diesel engines don’t have a coil to provide an ignition signal for the tachometer to measure, we are forced to find other ways to get a signal that’s proportional to engine rpm. One way to get a signal would be to use the “P” connection on the 140-amp (CS144) alternator’s “SFLP” plug.