So I have a 1993 WD21 Pathfinder. Thanks to the previous owner the Tachometer does not work what so ever. How you ask? Well the kid had the incorrect battery(reverse terminal) without a hold down and let the positive post contact the fender a few times(it may have taken a few things out honestly).

Now you are wondering what I have done already? To start i have corrected the battery. I have also bought multiple intrument clusters with supposedly working tachometers. Some were from a junk yard so who truly knows. I have installed each one and have had no luck at all.

For those that have dealt with this what have you been able to do to fix said issue? Currently I'm at a stand still. I also understand that the ECM could have an internal issue since it sends signal to the Tachometer.

On older Nissans without a crank sensor, the tach signal usually comes from the ECM, which in turn gets it from the 120-degree REF signal in the camshaft sensor. If that wasn't working I would think the truck wouldn't run, so there's probably an issue with the wiring between the ECM and the tacho, or the ECM has a blown tach output. A voltmeter should be able to tell you. With the truck running, you should see a "middle voltage" on the tach signal wire at the ECM. If it's flatlined at the same voltage with the engine running or stopped, the problem is most likely in the ECM. If it isn't, see if the signal is still there at the cluster end. If not there's a break in the wire between the ECM and cluster.

So I decided to go ahead and buy a used ECM(correct model for mine of course) and take a chance. Come to find out I did have a bad tach driver. Chances are the last owner took it out by accident by letting the battery flop around(and having the wrong terminal orientation). Now the tach works and im a happy camper!!

Nice!!