I have an 86 LJ70 with a 2L diesel. The tach is not functioning. I originally thought the culprit was the printed circuit on the dash because it was pretty much toast and only one of my gauges was working. I finally found a circuit board in Italy and replaced it and now all of my gauges work except the tach. I have two tachs so I tried both and neither functioned. I then went to the sender which is located in the injection pump and replaced it with a new OEM sender. Nothing. Tried both tachs. nothing. My question is how does one check the signal from the sender to the tach to see if the signal is coming thru and correct??? I have heard you need an oscilloscope. Is this true or is there another way to test it? I would think that out of 2 tachs, one would work, but just in case does anyone have a working tach for this configuration and for diesel? Sorry, can't get a photo to upload. I will try later, but the configuration is the same for all 70 series from 1984-1995 w/diesel.