620 Headlight Wiring

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Early Datsun 620 used switched-earth headlight wiring, along with a relay. Later 620 was made more reliable to discarding the relay and use power-switch headlights.

4-headlight system

High - 4 lamps light up (high filaments)
Low - 2 lamps light up (low filaments)

So the low beams go OFF when the high beams come on. All four headlamps with light, but only on the high circuits.

Circuit

Power for the headlamps comes via the Fuse Box, specifically the 'L' (lamp) fuse. The headlight switch provides power OUT when pulled to the 3rd position. From there power goes to the Dimmer Switch on the steering column. Depending on the lever position power is switched to the High Beams or the Low Beams.

1974 620 lighting diagram

LOW  - RB wire (Red wire with Black stripe)
HIGH - RW wire (Red wire with White stripe)
GROUND - headlight sockets are grounded at body Horn earth point
         via engine room wiring harness

Fuses

Power for the headlamps comes via the Fuse Box, specifically the 'L' (lamp) fuse in the Fuse Box.

'L' 15A head Lamp fuse
* High beams
* Low beams
* high beam pilot lamp in dash cluster

The Parking lights are on their own fuse. But still goes through the Lighting Switch. Headlight fuse can be burned out and P light work fine.

'PT' 10 AMP Park lights, Tail lights
* Meter illumination lamps in dash (except T/S and high beam lamps)
* Parking lamps
* Taillights
* Engine room lamp (only works with light switch pulled out)

Stop lights and Hazards on yet another fuse.

'H' 15 AMP Horn, Stop lights, Hazard lights 

Reverse lamps on a different fuse.

'M' 10 AMP Meter, Reverse Lights, Alternator Regulator 
* Reverse light

The Room Lamp is independent of headlight circuit. It doesnt go through the Lighting Switch. It has its own fuse.

'C' 15 AMP Radio, Clock, Cigarette lighter, Room lamp

Turn signals?

Stop lamps?