1974 Datsun 260Z — Wire-by-Wire Rewiring Plan

The literal first session: battery physically installed and both its cables made up. Nothing downstream exists yet, so the positive end is capped — but the battery side of the wiring is DONE after this phase.

Parts for this phase

• Custom battery cables from a battery shop (O'Reilly, NAPA, or local battery store) — they cut to length and hydraulic-crimp proper terminals while you wait. Better crimps than DIY, zero waste, ~$10–20 per cable. Bring your measurements (see below).
• Z Car Depot braided ground straps ×3 (~$6 ea)
• Battery + tray + hold-down
• Star washers, wire brush / sandpaper

Measure BEFORE you go to the shop

Use string or flexible tape, add 2–3" slack to each:

Get all four made in one trip — the starter cable isn't used until Phase 4 but it's the same shop visit.

Steps

1. Mount battery + tray; secure hold-down.
2. Battery − → chassis: install the shop-made negative cable. Wire-brush the inner fender bolt hole to bare metal, star washer, bolt tight.
3. Engine block → chassis: use a Z Car Depot braided strap from a block bolt to a clean chassis/frame rail point. This carries starter AND alternator return.
4. Chassis → body bond if EZ panel grounds to body. Install the shop-made bond cable.
5. Battery + cable: install the shop-made positive cable, route it toward the SafetyHub's future location. Cap/tape the far end and secure it — it lands on the SafetyHub's main fuse in Phase 2.
6. Leave the + terminal disconnected at the battery post until Phase 2's test.
7. Set the starter cable aside for Phase 4.

1. Mount the Blue Sea 7748 SafetyHub (old fusible-link area) and the True Mods relay box next to it on a shared plate/bracket.
2. Battery + cable → SafetyHub main input through the Blue Sea 5191 MRBF 100A at the battery post.
3. Populate SafetyHub MIDI fuses (charge 80A, EZ feed 50A, fan 40A) and ATO fuses (headlights 30A, blower 25A, horn 15A, inspection 5A).
4. SafetyHub EZ-feed branch → EZ panel main input.
5. Mount EZ panel inside, accessible.
6. Run short 10 AWG jumper feeds from SafetyHub branches to relay-box relay 30 terminals.
7. Run relay grounds to the SafetyHub's built-in negative bus.

Use crosswalk B. Key points:

• L runs through the dash charge lamp (excitation path), other side = switched-IGN.
• Add the S (yellow) sense wire to +12V — EZ doesn't supply one.
• Charge wire from BAT → the SafetyHub 80A MIDI; size both to 60A.
• No external regulator, shunt-to-regulator, or fuel-pump-cut relay.

Known gotcha: if the alternator doesn't start charging until high RPM (~3,500 rpm), the L excitation path is weak — check the charge lamp bulb (correct wattage, not burned out, not LED without a parallel resistor) and the S sense wire connection.

The Datsun ignition switch is a known weak point — running the full load through it wears and melts the contacts. Offload it with a relay.

1. Land EZ BAT/IGN/ACC/ST on the Datsun ignition switch (crosswalk A).
2. Ignition relay (offloads the switch):

Starter: 4–6 AWG heavy feed → starter B+; EZ ST → solenoid trigger (18 AWG).

1. Coil + resistor: switched-IGN → ballast → coil + (ref BW/BL/L, Fig 14:4). 10 AWG.
2. Distributor / igniter per ignition type. 10 AWG for primary.
3. Sensors: water temp, oil pressure, thermal transmitter → gauge/lamp wires. 18 AWG each.
4. Carb fuel feed (now): small dedicated circuit for the current pump — separate from Phase 13's dormant feed.

Heavy cyclic load — own relay, own SafetyHub branch. Wire after the engine runs so you can test it hot.

• Optional manual override toggle: 3-position OFF / AUTO / ON dash switch.
• Fan ground straight to clean chassis.

Mechanical fan removal: remove shroud (top + bottom), then fan and fan clutch off the water pump. Use a water pump pulley bolt kit (electric-fan conversion).

Reference guides

• Skillard — Electric Fan Conversion for the Datsun S30Z
• ZCarCreations — Z Car Electric Fan Install
• The Z Store — Dual 12" Electric Fan & Shroud Kit
• Z Car Depot — 12" fan + shroud

Per relay (LOW and HIGH)

• Keep fuses on the output side (10A H.L / H.R, Fig 14:10).
• 260Z headlights are ground-switched at the dimmer — confirm with the meter whether EZ's HI/LO output switches (+) or (−) before you commit terminal 86.

Reference: "Dave's harness" diagrams at ClassicZCars

• Fig 14:11. GW = running-light feed → front combination lamps, side markers, rear markers, license.
• Map EZ TAIL/PARK circuits; ground each lamp locally.

Engine bay / inspection lamp

• Tiny single-bulb load — its own small EZ panel circuit (≈5A), no relay.
• Feed constant-hot (not switched-IGN) so it works key-off during engine work.
• Factory-style on/off: constant 12V to the lamp, switch built into the fixture.
• One 10 AWG feed wire + a local ground.

Biggest phase — one gauge at a time. Two parallel paths — pick A or B.

Common prep (do this either way)

• Switched +12V (ignition-on) to the cluster — 10 AWG
• (−) ground — the dedicated 10 AWG dash ground bus back to chassis
• Illumination +12V → EZ dash-light/dimmer circuit — 10 AWG
• Charge lamp → alternator L (Phase 3) — 18 AWG

Path A — Factory gauges (wire now)

1. Land EZ gauge circuits on the factory cluster.
2. Wire + test individually: tach → speedo → fuel/amps → temp/oil → clock.
3. Factory senders feed factory gauges.

Path B — Speedhut-ready (defer the gauges, prep the dash)

• Speedo → GPS unit. No VSS or cable needed.
• Tach → single signal wire from the coil (−) to the cluster; leave it stubbed.
• Temp / oil / fuel → use Speedhut's own senders.
• Voltmeter, not ammeter — route a sense wire from switched +12V.

Ammeter delete (recommended either path): the factory ammeter routes full charging current up to the dash and back — heavy current on aging wiring behind plastic. A voltmeter only senses voltage, removing the hazard.

EZ brake gotcha + 260Z fix

• EZ supplies three brake wires and routes the feed through the turn-signal switch (GM logic).
• 260Z brake circuit is independent. Ignore EZ's TS routing: orange feed → brake pedal switch → straight to rear brake lamps. 10 AWG.
• Flasher + hazard units per EZ; combo TURN L/R (crosswalk C) → front/rear signals.

Horn (Hella Supertones, ~10–12A for the pair)

• A horn relay is not optional and never was — the factory 260Z already used one.
• The EZ-21 kit includes a horn relay + connector. Verify yours is present.
• Any standard cube relay (30/40A) handles ~12A. Horn fuse: 15A on its own ATO branch.
• On the Datsun the button switches (−) ground, so coil 86 = constant (+)12V and 85 = switched ground from the button.

1. Identify Honda terminals by applying power and watching behavior: low, high, park/cam, ground. The park wire returns blades to the bottom on switch-off.
2. Map to EZ wiper circuit if speeds line up; park circuit ties to the EZ wiper switch's park terminal.
3. Check draw: usually higher than stock. Compare stall current to the EZ wiper fuse — if marginal, drive via a relay.
4. Washer pump (if used) on its own EZ circuit.

Heater-only: fed blower + control panel. Blower is continuous — own relay + SafetyHub 30A ATO branch.

• Speeds via the Vintage Air resistor pack or controller.
• No A/C: skip compressor clutch, binary/trinary switch, condenser-fan trigger.
• Heater control valve (coolant) is mechanical/cable — no wiring.

Pull the oversized rear feed ONCE. Nothing energized now.

1. Power: 10 AWG SafetyHub → rear. Terminate, label "EFI PUMP +", leave disconnected.
2. Ground: 10 AWG to clean rear chassis.
3. Trigger: 18 AWG rear → engine bay; engine-bay end accessible + labeled (future ECU pump output).
4. Relay + fuse out for now; final 30A SafetyHub MIDI + relay with the pump.
5. Carb pump runs on its Phase 5 circuit.