Installed new tach after a final verification that the wiring was good. Didn't work. I made up a few words you haven't even heard yet! Started playing with the two tachs, comparing new circuit boards to old tach (found a dark did colored spot on old...it was fried).
Long story short, the circuit board can only go on one way. Then you put the little washer over each of the 4 prongs, followed by the little lock washer, then the nut. Next put on the plastic backing that screws into the cluster housing by 3 screws...then plug in wiring harness to the three prongs sticking through the backing. Screw plastic backing into housing, then screw in the tach itself.
My mistake? I put the nuts on the outside of the plastic backing to hold the tach to it...that was a bad idea apparently. The only thing holding that backing to the tach is the harness plug! Who knew!?!
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