Lighting
Most S30 lighting is straightforward — but two things are worth knowing up front: the dash headlight switch carries the entire headlight current load, and it melts; and the combination flasher handles both turn signals and hazards together. Understand those two and you understand most S30 lighting trouble.
Please treat every year-specific claim, resistance value, or pinout on this site as a starting point — not a substitute for the FSM for your specific car. Each page has a Sources & verification section at the bottom; please tell us when you find anything wrong.
Headlights
The S30 uses two round 7" sealed-beam headlamps. Each lamp has a high beam and a low beam filament; both are switched at the dash via the headlight switch (on/off) and the column stalk (high/low + flash-to-pass).
The full lamp current — both lamps, both filaments capable of ~10A combined — runs through the dash switch and the column stalk. There is no relay in the factory wiring. Over time, the contacts in the dash switch heat up, oxidize, and eventually melt.
The headlight relay upgrade
The single most popular S30 electrical mod. The idea: leave the dash switch in place but use it only to trigger a pair of relays that carry the actual current. Add a fused power feed direct from the battery to the relays. Result: the dash switch carries milliamps instead of amps, voltage at the bulbs goes up by ~1V (brighter light), and the original-looking dash is preserved.
Parts list
- Two 4-pin or 5-pin Bosch-style 30/40A relays
- One 30A inline fuse holder (for the battery feed)
- ~6' of 12 AWG wire for the high-current path; ~6' of 18 AWG for triggers
- Spade connectors and a relay socket pair (or pre-built socket harness)
Wiring
- Pin 30 (common) on both relays: tie together and run a fused +12V from battery + through a 30A inline fuse.
- Pin 87 (NO) on the low relay: connect to the original R/W (low beam) wire that used to come from the column dimmer. Cut the existing wire and tap in.
- Pin 87 on the high relay: connect to the original R/Y (high beam) wire, same way.
- Pin 86 (coil +): on each relay, connect to the original wire that used to feed the lamp. Now it just triggers the relay.
- Pin 85 (coil −): ground both to a known good chassis ground.
- Mount the relays on the inner fender or core support, away from direct exhaust heat. Sleeve the trigger wires to keep them tidy.
Several vendors (Dave's Z Garage, MSA, eBay sellers) sell pre-made plug-and-play relay harnesses with the correct connectors for the H4 conversion or stock sealed beams. Cheaper than your time, and the connectors match factory.
Turn signals & hazard
The S30 uses a thermal flasher relay (the "can") that pulses with a duty cycle dependent on bulb load. Key behaviors:
- If the flasher is too fast (hyperflash), one bulb is out — the lower load shortens the heating cycle.
- If it's too slow or stuck on, the flasher itself is failing.
- Hazards use a separate flasher can on most years; some 240Z combine them.
If you upgrade to LED tail/turn bulbs, you must use a load-resistor or replace the flasher with an electronic LED-compatible flasher, or it'll hyperflash.
Brake & tail lights
On the S30, tail/brake/turn share a single dual-filament bulb on each side. The combination switch in the column directs current intelligently — if you're indicating a turn while braking, the brake circuit is interrupted on that side and the turn signal flashes alone.
This is implemented in the column combination switch contacts. A worn switch can cause weird symptoms: brake lights stuck on with the indicator running, or the indicator stops flashing during braking.
Dome & courtesy
The dome lamp lives on a switched +12V from the body harness; the door pin switches connect the lamp's ground side to chassis. So the bulb is always hot — closing a door "opens" the ground and turns the lamp off.
If your dome stays on with doors closed: door pin switch sticking, or the rubber boot has perished and is shorting the pin to chassis.
Wire colors used in lighting
| Wire | Color | Function |
|---|---|---|
| R/W | Red / white | Headlight low beam |
| R/Y | Red / yellow | Headlight high beam |
| G | Green | Tail / parking lamp |
| G/W | Green / white | Brake (stop) lamps |
| Lg | Light green | Right turn signal |
| Lg/B | Light green / black | Left turn signal |
| B | Black | Ground (always, on Datsun) |
Common failures
Melted headlight switch
The classic. Symptom: dim headlights, intermittent operation, sometimes only one beam works. Pull the switch and inspect the back — discolored plastic, melted contacts. Fix: do the relay mod, then either replace the switch with a reproduction or carefully clean and reuse the old one (it's no longer carrying load, so it'll last forever).
Combination switch wear
Symptom: turn signal doesn't self-cancel, high beam intermittent, hazard doesn't work but indicators do. Reproduction column switches available. Cleaning sometimes works — disassembly is fiddly but documented.
Tail light socket corrosion
Symptom: dim tail lights, brake works but turn doesn't, gauge ground gets weird (yes, really — bad tail light grounds backfeed into the gauge cluster ground via the tail circuit). Fix: pull sockets, clean contacts and bayonet bases, dielectric grease, reinstall. Refresh the tail light panel ground.
Dim & flickering brake lamps
Brake light switch on the pedal box wears. Symptom: brake lamps come on weakly or only when you really press hard. The switch is a simple plunger and is cheap to replace.
Sources & verification
Claims on this page should be cross-checked against:
- Nissan FSM — Body Electrical (BE) chapter, lighting section, for your specific year and market. Free PDF scans at xenons30.com.
- Atlantic Z Car Club — "Headlight Relay Modification" tech article and other lighting write-ups.
- classiczcars.com — forum archive, headlight relay mod threads, tail light grounding diagnostics.
- s30.world / Parts & Tech — part history, including market-specific lighting differences.
Spot something incorrect? Drop us a note.