Dash board doesn't light up - 1991 Nissan Pickup

Has to be a fuse or the interior lighting relay, unless you cut any wire's, only other thing is fault on the PCB in the dash, doubt that though.

Remove dash to the bulb components (the layer of dash with only bulbs[looks complicated]) turn dash lights on and identify wich bulbs are not working, replace them with the correct bulbs. if this is unsuccesfull find the connection from the bulbs to the wire and also the connection from the wire to switch. ensure the components inside the connextions are clean(pull apart and check for rust, dust, dirt ect..) you can buy connection cleaner from most car orrientated shops.