+1 to the multimeter (volt/ohm meter). Without this, chasing problems in an electrical circuit is like looking for a acorn on a moonless night.
The following might not exactly match the wiring on a RE but the basic principles should be right.
If the parking lights (casquette eyes and tail light) are working with the headlight/parking light/off switch in the parking light position that would indicate the switch is getting power from the keyed ignition switch.
This switch should have at least a power in, parking lights out, headlight out terminal or wire.
Changing this switch to the "Headlight position" I would then check the headlight output terminal at that switch to see if the switch was working correctly. If there is power coming in but no power out, the switch is the problem.
If the headlight power output terminal is powered with the switch in the "headlight" position, the next thing to check is the High/Low beam switch.
Is the power getting to its input terminal? If it is, check the high/low output terminals at that switch.
If the High and Low beam output terminals can be turned off and on by changing the switch lever, the problem is the wiring between that switch and the headlight.