If under dash light works, it confirms there is current coming out of service light dimmer switch. When you say bulb is "not blown", I'm assuming you tested it and it is OK. If this is the case and it is not coming on, then it could be a problem with dimmer part of headlight switch. You will need that volt meter or test light to proceed much further.
If under dash light works, but you have no dash lights, it is possible that all the bulbs are burned out or have bad contacts to the plastic sheet the dash circuit is on, also possible the contacts need to be cleaned where wires plug in to cluster assembly. 35 years of dust, corrosion and possibly a little mouse urine can easily break these small contacts.
On all the CUCVs (and other trucks of this vintage) I get, I take the dash pad off and clean up accumulated matter and clean contacts, lube heater cables, etc. It takes a little time, but worth it in my opinion.