How to Wire the Ignition Switch in a 1967 Ford Mustang Step by Step Guide

For accurate restoration or troubleshooting, locate the purple/white wire (starter solenoid signal) and trace it from the steering column harness to the firewall grommet. Terminate it at the solenoid’s “S” terminal–verify continuity with a multimeter set to 200 ohms. A common failure point is the neutral safety relay (N.S.S.) on early models; bypass it temporarily to isolate issues, but replace it if resistance exceeds 5 ohms.

Wire colors on the P60 pigtail (behind the instrument cluster) dictate functionality: yellow (accessory), green (coil positive), and black/white (ground). Cross-reference with an original Ford service manual (part #C6ZZ-12650-A) for terminal IDs–aftermarket reproductions often mislabel the I/S (ignition-starter) circuit. Use a 10-gauge fusible link (not standard fuse) between the battery feed and the amplifier relay to prevent melting the fusible wire during voltage spikes.

Check the vacuum advance connector (orange/black) for corrosion–disconnect it at the distributor before testing resistance to ground (should read infinite). If the tachometer flickers during cranking, the ballast resistor (1-ohm, ceramic) may be cracked; solder in a new 10-watt resistor to prevent coil burnout. For automatic trans models, ensure the start inhibitor switch (neutral safety) has less than 0.5V drop across its contacts in “Park.”

Use heat-shrink tubing (not electrical tape) on all splices, especially near the exhaust manifold where temperatures exceed 150°C. Scan for intermittent shorts by wiggling the harness near the steering column collar–if the engine stalls, the flexible conduit has frayed wires requiring replacement of the entire column-to-firewall loom. For aftermarket push-button starters, wire the momentary switch in parallel to the factory solenoid circuit, not in series, to avoid voltage drop.

Classic Ford Coupe Electrical Connection Guide

Locate the central harness bundle beneath the dashboard on the driver’s side–it houses black, purple, red, and green wires, each terminating at a specific terminal on the back of the assembly. The black lead connects to the “BATT” post, delivering uninterrupted power from the battery. Purple and red wires attach to “IGN” and “ACC” respectively, activating circuits when the key rotates to corresponding positions. Ensure the green wire, linked to the “ST” terminal, sends a 12-volt signal to the solenoid only during cranking.

Verify wire gauge before reconnecting–primary leads should be 12 AWG, with the starter trigger line using 10 AWG for adequate current handling. Strip insulation precisely 5 mm; excess bare copper invites short circuits under vibration. Crimp terminals securely using a ratcheting crimper, then solder junctions for corrosion resistance. Heat-shrink tubing over each joint prevents moisture ingress, a common failure point in older vehicles.

• Black: direct battery feed (no fuse)
• Purple: ignition system (powers coil, gauges, fuel pump)
• Red: accessories (radio, interior lights)
• Green: starter engagement (temporary 12V pulse)

Test continuity between the assembly’s “BATT” post and battery positive with a multimeter–expect less than 0.5 ohms resistance. If readings exceed 2 ohms, inspect the fusible link (a 14-gauge wire with a melted segment) or corroded connections at the firewall bulkhead. Replace the link if melted; Ford used a 60-amp rating for this circuit, and undersized alternatives risk overheating.

Common Failure Symptoms

1. Key turns freely without engaging starter: worn actuator cam inside the assembly–replace the entire unit.
2. Radio functions but engine won’t crank: broken purple wire at the firewall or faulty solenoid.
3. Intermittent power loss: loose terminal at the back of the assembly–tighten with a 5/16” nut driver.
4. Headlights dim during cranking: weak battery or ground strap between engine and chassis isn’t sufficient–upgrade to 4 AWG cable.

Route wires away from exhaust manifolds and steering column mechanisms; high heat degrades insulation over time. Secure harnesses with nylon zip ties every 6 inches, avoiding metal edges that can chafe wires. If replacing the original harness, match wire colors exactly–aftermarket kits often deviate, complicating future troubleshooting.

For push-button starter conversions, splice the green wire into a momentary switch, then wire the switch’s other terminal to the “ST” post. Use a relay rated for 30 amps to protect the assembly from backfeed. Add a diode across the relay coil to suppress voltage spikes, which can damage sensitive electronics downstream.

Reassemble the lower dash panel only after confirming operation–misaligned wires can bind when the panel is reinstalled, causing premature failure. Store a spare 5-terminal replacement assembly (Ford part C5ZZ-11572-A) in the glovebox; these often fail without warning and are difficult to source roadside.

Locating the Proper Connection Points on a Classic Ford Starter Control

Begin by locating the five-metal-contact assembly at the rear of the column-mounted activator. The uppermost terminal, marked “BAT” (battery), is the primary power feed and must connect directly to the 12-volt positive lead from the fuse box, typically using 12-gauge red wire with a yellow stripe. Verify continuity with a multimeter before securing the connection–no resistance should register above 0.2 ohms.

The second terminal from the top, labeled “IGN” (ignition), supplies power to the coil, electronic accessories, and instrument cluster. Route this circuit through a 10-amp fuse using 14-gauge yellow wire with a black tracer. Avoid splicing into this path for aftermarket add-ons; instead, tap the “ACC” terminal for non-essential circuits to prevent voltage drop during engine cranking.

Accessory and Starter Circuit Identification

The third terminal (“ACC”) delivers current to the radio, heater, and power windows only when the key is in the “on” or “accessory” positions. Use 16-gauge pink wire for this branch, ensuring it bypasses the ballast resistor to maintain consistent voltage. Test functionality by engaging the key to “ACC” while monitoring voltage at the radio’s power lead–readings should stabilize at 12.6 volts.

The fourth connection (“ST”), positioned just above the ground terminal, energizes the starter solenoid exclusively during cranking. This wire, usually 12-gauge purple with a white stripe, must run directly from the activator to the solenoid’s “S” post without intermediate junctions. Confirm correct routing by observing a clean 10-12 volt surge at the solenoid when the key is turned to “start,” followed by an immediate drop to zero once released.

Finally, the bottom terminal (“GND” or “I”) serves as the ground reference for the entire system. Attach this to the firewall using a 10-gauge black wire, securely fastened with a star washer to prevent corrosion-induced voltage irregularities. Check ground integrity by measuring less than 0.1 volts between this terminal and the negative battery post while the engine runs at 2,000 RPM.

Use a factory service manual illustration to cross-reference terminal positions, as aftermarket replicas often deviate by 1-2 mm. Label each wire with heat-shrink tubing before final assembly, noting the color code and destination on a waterproof tag to simplify future diagnostics.

Step-by-Step Guide for Installing a New Starter Control on a Classic Ford Pony Car

Disconnect the battery terminal marked with a minus symbol to prevent short circuits. Locate the column-mounted activator beneath the steering wheel–it’s secured by a single retaining ring behind the bezel. Use a Torx T-20 driver to remove the two screws holding the lower dash panel; this exposes the wiring harness. Tag each wire with masking tape labeled A through D (A: red/light green stripe, B: purple, C: yellow, D: black) to match the factory schematic. Strip 1/4 inch of insulation from the ends of replacement leads before crimping spade connectors.

Wire Code	Color Pair	Terminal Location	Function
A	Red/Lt Green	Bottom slot, left	Starter solenoid
B	Purple	Top slot, center	Accessory power
C	Yellow	Middle slot, right	Ignition feed
D	Black	Ground screw	Chassis ground

Align the new activator’s mounting plate with the existing column bracket holes; secure it using the original screws. Snap the bezel back into place, ensuring the retaining ring clicks audibly. Reattach the tagged wires to the corresponding terminals–confirm each connection with a gentle tug. Reconnect the battery terminal; test the system by rotating the key to the start position–listen for the solenoid click. If absent, verify the red/light green wire connection to the starter relay under the driver-side fender.

Frequent Errors When Hooking Up the Classic Pony’s Starter Circuit

Avoid crossing the red “I” terminal with the white “A” lead–this mistaken swap fries the solenoid coil instantly. Factory schematics label the red wire as constant 12V hot, while the white conductor only energizes during cranking. Reverse these, and the solenoid pulls full current continuously, burning open in under ten seconds.

Snipping the yellow resistance wire to shorten it disrupts voltage drop calculations. That 1.5-ohm resistor feeds the coil; honoring its length maintains 6-9V at the distributor. Splicing instead of replacing the entire harness with OE-spec resistance cable causes hard starts and fouled plugs by week three.

Skipping the bulkhead connector grounds the accessory circuit through the firewall. Corrosion at the firewall grommet eats 0.3V, starving the radio and gauges. Always attach a dedicated ground strap from the harness to the frame rail; paint-stripping just the bolt threads isn’t enough–grind down to bare metal for a 0.1-ohm connection.

Jumpering the purple “S” wire straight to battery positive bypasses the neutral safety switch. This mistake lets the engine crank in gear, destroying the starter bendix in under 500 milliseconds. Verify the neutral switch closes only in park or neutral by probing with a multimeter–any reading below 0.3 ohms indicates a shorted switch that needs replacement before wiring.

Relying on aftermarket wire colors instead of factory labels invites cross-ups. Reproductions often swap orange and dark green; connect them backward, and the fuel pump runs constantly, flooding the engine. Use a 5A fused light tester to trace each circuit back to the fuse block–original Ford documents list every wire’s gauge and function, not just color.

Forgetting to crimp terminals before soldering creates brittle joints. Heat shrink must cover the entire splice; otherwise vibration cracks the solder, causing intermittent cut-outs at 3,500 RPM. Apply heat just until solder wicks–excess heat melts the insulation, shorting adjacent circuits. Test every connection with a 12V load; voltage should never drop below 11.7V across any wire.