I had flickering headlights and flickering dash illumination separately, about a year apart. So it is possible you have two problems, but not necessarily.
Starting with the easiest thing first, I would suggest the following (mostly as already suggested by self and others):
- Lighting Switch - pop from dash, remove and replace the connector at the back; squirt of electical contact cleaner.
- Dimmer Switch - pop from dash, remove and replace the connector at the back; squirt of electical contact cleaner.
- Instrument pod - remove dash lid, then pull and replace all three/four(?) connectors. Take the opportunity to replace any blown instrument illumination lamps while you are there.
- Headlamps - ensure wire clips are in good shape and properly fitted; remove units to bench if necessary.
- Ignition switch - OK in my experience but suggested by someone else as a likely cause.
- Voltage regulator - unlikely in my opinion.
- Other wiring/connectors/components.
You must try (1) and (2) first. I recall there was a nack to coaxing the switch & rheostat from the dash but can't remember the details. Are there a couple of pinch-barbs round the back of each? Anyone?
(1) - (4) are things that I've done in the past to help recover my lighting. They are all reasonably simple and will cost little more than your own time.
(1), (2) & (3) were undertaken together, therefore not really possible to say which was the culprit part. They collectively cured my dash flicker. (3) cured my headlight flicker. (5) - (7); just attempting to summarise other people's (no doubt excellent) suggestions.