I installed a full guage package on my 2023 RTV X1140. I have done tach, EGT, boost, oil temp, oil pressure, water temp, volts, HST fluid temp, and am working on a HST pressure guage now using a HPOP guage and an older Ford ICP sending unit.
For the tach, use a diesel specific tach. These are meant to read pulses from the alternator. For mine, I removed the alternator, ran a wire from 1 of the 3 rectifier leads to the tach. I used a GlowShift 5000 RPM diesel tach. The diesel tachs will need calibrated by using the 2 calibration screws on the back of the guage. Use a non contact tachometer to get the RPM from the crank pulley and adjust diesel tach to match the non contact tach. Most guage manufacturers make a module that can mount to the outside of the alternator to pick up the pulse signal if you are uncomfortable disasssembling and adding a wire inside your alternator. I have one new in the box I would sell for 1/2 price. Got it in case I could not get the alternator modified correctly but it was actually really easy.
Drop the skid plates for easy cable routing. As for accuracy, I think I am within 6 - 10 RPM between diesel tach and non contach tach readings. It is accurate for me +/- 10 RPM from idle at 1500 RPM to 3600 RPM where I have my high adle set at.
