The instrument cluster lights' are powered from the long 14-point
connector that plugs in to your cluster on the right side. Position #3 is
the power for the 3 instrument cluster lights.

My guess is that you have a bad connection on the cluster's connector.
It's possible that the copper foil for #3 on the blue printed circuit
plastic is worn, or the connector may be bent at that spot and not making
good contact.

Michael