The Hewlett-Packard 59306A is an HP-IB relay actuator with 6 SPDT relays.
The front push-buttons contain tiny bulbs for illumination. These can burn out over time, but replacements are still available. The bulbs are 5V 0.06A in a "T-1 3/4 standard midget flange" form, suitable replacements are JKL-7333, CM-7333 or similar.
The "power" and "remote" lights contain bulbs with wire terminals, rated for 6V and 0.04A. These can be replaced with JKL-1730 bulbs or similar.
- Peter Holzleitner - Hewlett Packard Relay Actuator — a good description of the 59306A and other useful information.