Tachometer reads below 0

[MJKally]

I'm working on getting my 1990 4.0 Comanche back on the road, it's sat for 20 years and many things aren't working. The entire gauge cluster was dead, so I recently took it out, cleaned all the contacts and checked them all for continuity. The gauges mostly work now, except my tach is reading below 0 when the engine is running. If I give it some gas, the needle does go up, but the resting position while it's running is this: 

 

 

I have an original service manual with electrical diagrams, but it doesn't make it obvious where the wiring for the tach goes, or what to do if it's out of calibration. I've already gone through and cleaned as many grounds as I could find, all the connections in the IP seem to be good now. What would cause this? 

[Eagle_SX4]

It is a good sign that the tach moves when revving the engine. That means the needle was probably removed at some point and put back on incorrectly. With the engine off, take the plastic lens off the cluster then simply pull the needle off with your fingers then press it back on while aligning it to zero.

 

I had the same issue when I got my truck. Although it was clear my gauges had been messed with as there was aftermarket gauge faces on it. The gauge faces on yours are original.

[MJKally]

I had the whole cluster apart to clean the contacts last week, I didn't remove the needle but it's possible I knocked it or disturbed it while it was apart. I'll try that, thanks!

 

I've ordered a renix engine monitor, so I can check to see if it's calibrated with that whenever it turns up.