Yamaha Digital Multifunction Gauges - No Tach Function Working

I have two Yamaha Digital Multifunction gauges, Tach and Speed on a used boat I've been working on. The gauges look like from the 1990's, and they worked fine when I water tested them. Then I started to work on the changing the center console gauges positions and so I disconnected both gauges. I also disconnected all the cables, hoses, and connectors at the engine to run them all through a rigging tube. After I connected everything, the tach does not display any numbers, it only backlights. The Speed gauge has everything working. I connected everything as it was before (and it is according to the wiring diagram I pulled online), but now the tach shows nothing but backlight. Can someone advise me what to do next? I have a good multimeter.

Ok, I got it fixed. I connected the Tach gauge power wire (yellow) and the black ground wire directly to the battery with some alligator clips and wires and it turned on. Went back and tested the connections and found a problem with the ground connector. Fixed it and all is fine now.