head lights
Are they
flashing after they've been turned on for a time, or are they
flickering randomly or are they
pulsing in time with the movement of the ammeter needle? If they're flickering, then the trouble's faulty wiring, a faulty connection, and/or faulty headlight or beam-selector switches. If they're pulsing, then the trouble's in the charging system: high resistance in the alternator field circuit, faulty voltage regulator (or the regulator's fine but it has an inadequate ground), worn or faulty alternator brush(es).
If they're actually flashing, the thermal-cutout circuit breaker built into the headlight switch is tripping because it's grown "soft" with age and/or your headlamps are drawing more current than the switch is rated for. See the Allpar link already provided or
this page.