all my dash gauges and idiot lights are working but i have no dash lights on 1990 Chevrolet Astro

someone told me it might be a four-prong relay. Do you have a location and test method? Bulbs are all ok

Asked by for the 1990 Chevrolet Astro
there is a separate 7.5 amp fuse for the dash light. they work off the headlight switch.

how do you know the bulbs are good??