Cluster ground plug in

[ray_mcavoy]

That sounds like you might be describing the fiber optic cable that is used to illuminate the windshield wiper switch ... I believe that was a 73/74 only thing, with 75-up going to a separate bulb for the wiper switch.

Some of the earlier years used a similar fiber optic to illuminate the automatic trans shift indicator on the column. And others used it to illuminate the ash tray.

Anyway, the upper end of that fiber optic cable should be attached to a special socket that that twists (quarter turn) into one of the bulb openings. That special socket should also hold a #194 bulb and be installed into one of the cluster illumination locations ... doesn't matter which one as long as it will reach and is a cluster illumination (not turn signal indicator, high beam indicator, warning light etc.) location.