If the needle doesn’t move at all when you turn the ignition on, you will have to remove the gauge “again” and bench test as Otto suggested.
When you installed the gauge, did you check to see if the trim piece interfered with the needle?
Some of the reproduction gauges are made slightly thicker and the needle gets caught on the inner trim piece inhibiting the needles movement, making the gauge look like it’s not functioning. If you find this condition, a gentle push with your fingers will give you the additional clearance you need to keep it from binding. Mind you I do mean gentle as it moves easily and you don’t want to distort the inner trim piece.
I know what a pain it is to have to remove and disassemble the cluster as I had to do it three times myself before I got my gauge to function properly. To help with removing the cluster, I replaced my nuts with brass knurled nuts from the hardware store which makes them so much easier to remove and reinstall.
