510 Headlight Wiring

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Datsun 510 uses headlights that are always hot, but not connected to ground until the Lighting Switch is pulled.

510 Switched-Earth Wiring

Headlights are not permanently grounded as in newer Datsuns
Headlights are permanently connected to HOT via the Fuse Box

Original 1968-1969 6-fuse fuse box
One fuse powers both Headlights

1969-1973 Dual-Fuse Headlight Circuit

New for 1969 8-fuse modular fuse box
'HL' 10A RL Power to Left Headlights
'HR' 10A R Power to Right Headlights

Relay switches ground on for either
* High beams (all 4 lights) 
* Low beams (2 outer lights)
Relay does not switch the 12V HOT side
Relay switches the GROUND wires
Relay Coil is powered by GL wire from Lighting Switch
Relay Coil is switched by BR wire from Dimmer Switch
* ungrounded = Low beams switched to Ground
* grounded = High beams switched to Ground

Dimmer Switch
* Only connects to Ground (High beam position) or disconnected
* No 12V runs through it

Lighting Switch
* controls headlights, park lights, dash illumination lights
* does not control turn signals
* does not control dash pilot lights (OIL, CHG, P.B)

Dash Illumination Lamps (2) are grounded though Pin 2 Black wire. 
GW Pin 1 goes to Lighting Switch

OIL pilot lamp is grounded via Oil Pressure switch
G Pin 8 goes to 4-way Flasher Switch

CHG pilot lamp is grounded via Voltage Regulator
G Pin 8 goes to 4-way Flasher Switch

Parking Brake pilot lamp is grounded via Handbrake switch
G Pin 8 goes to 4-way Flasher Switch

Relay

Late relay

1969-1972: The two relays on the back side of the RH strut tower in front of the fuse box are for the headlights and the horn. The headlight relay has a 6 prong plug, the horn has four individual wires.

1973 relay is on the RH side behind the headlights

Original JIDECO relay

Low Beam Relay
B5230-28000

3-wire horn relay
Headlight Relay

Headlight Relay
B5230-89985

Relay Repair

Carefully pry the cover loose. there are four crimps, one on each side. uncrimp carefully with a screwdriver and remove the cover. Now between the contact on the bottom of the plastic piece is a screw. Remove it and carefully lift the guts away from the base and you should see rust on the bottom. Sand that clean apply so dielectric grease, reassemble and you should have a working relay. It's the rust and corrosion that is interrupting the circuit. Be careful of the wiring in the relay. The unit itself is pretty tough but some of those fine wires can break if you get too rough.

So, that's what I did...and now I have headlights! Thanks Bruce!