That wire, as I recall, had the contact held by a small insulator backing. It has a tendency to disconnect and separate. It should be there still, and you'll have to use an adhesive to make them one again. Then it'll maintain contact again.
The same thing happened to me as these wires are delicate in their old age.
I'd like to know how you got your bulbs in the instrument panel. I can't replace the bulb above the ignition switch let alone the rest.