1968 Mustang Ignition Switch Wiring Diagram

The intricate wiring harness of a 1968 Ford Mustang is a critical component, acting as the nervous system for its engine management. Among these complex circuits, the ignition switch wiring diagram holds paramount importance, governing the vital flow of electrical power that initiates the engine's operation. Understanding this specific diagram is not merely an exercise in automotive curiosity; it's a fundamental skill for any owner or restorer aiming to maintain, troubleshoot, or repair the core starting function of their classic Mustang. This guide delves into the essential aspects of the 1968 Mustang ignition switch wiring, providing clarity amidst the tangle of wires.

Introduction: The Heart of Starting The ignition switch in a 1968 Mustang serves as the primary command center for the vehicle's electrical starting system. Located on the steering column, it's the physical interface between the driver and the engine's ignition process. When the key is turned, it completes a circuit, allowing current to flow from the battery through the ignition switch, through the starter solenoid, and finally to the starter motor itself, cranking the engine. Simultaneously, the switch activates the ignition coil, enabling spark generation for the engine's cylinders. Deciphering the 1968 Mustang ignition switch wiring diagram is crucial because it maps out the specific connections, color codes, and pathways for these essential circuits. This knowledge empowers owners to diagnose issues like a key that won't turn, the engine failing to crank despite a good battery, or intermittent starting problems. It also provides the blueprint for safely installing new switches or modifying the starting circuit. Mastering this diagram transforms a seemingly complex electrical system into a manageable and understandable part of your Mustang's anatomy, ensuring you can keep your classic companion running reliably.

Steps: Navigating the Ignition Switch Circuit Understanding the 1968 Mustang ignition switch wiring requires breaking down its core circuits. The diagram typically illustrates several key connections:

1. Battery Positive (B+) Connection: This is the primary power feed. The large, often red, wire from the battery's positive terminal connects directly to the ignition switch's "B+" terminal. This wire provides the main source of electrical power for the entire starting circuit.
2. Ignition Switch Terminals: The switch itself has multiple terminals labeled (often) as "B+", "IGN", "ST", "ACC", and sometimes "BAT". The "IGN" (Ignition) terminal is the critical one for starting. When the key is in the "Start" position, this terminal connects to the "ST" (Starter) terminal via the ignition switch contacts. The "B+" wire connects to the "B+" terminal. The "ACC" (Accessory) terminal powers accessories like the radio and dash lights when the key is in the "Accessory" position. The "BAT" (Battery) terminal provides a direct battery connection when the key is in the "On" position.
3. Starter Solenoid Connection: The starter solenoid is the heavy-duty relay that engages the starter motor. The ignition switch "IGN" terminal connects to one side of the solenoid's coil. The other side of the coil is connected to the battery positive wire via a heavy gauge cable. When the key is turned to "Start", the switch contacts complete the circuit, energizing the solenoid coil. This creates a magnetic field that pulls a plunger, closing a high-current circuit between the battery positive and the large "S" (Starter) terminal on the solenoid, which then connects to the starter motor.
4. Ignition Coil Connection: The ignition coil requires high voltage to generate the spark for the spark plugs. The ignition switch "IGN" terminal connects to one side of the coil's primary circuit. The other side of the primary circuit connects to the battery positive wire via the ignition coil's "I" terminal. The coil's secondary circuit (the high-voltage output) connects to the distributor's "R" (Rocker Arm) terminal, which feeds the distributor cap and ultimately the spark plugs.
5. Neutral Safety Switch (NSS) Connection: Modern cars require the ignition switch to only work when the transmission is in Park or Neutral. While not part of the ignition switch itself, the wiring diagram will show the connection point for the NSS switch (usually a small, multi-pin connector near the clutch pedal or transmission shifter). This switch interrupts the ignition circuit if the car is in gear, preventing starting.
6. Key Lock Cylinder Connection: The ignition switch is physically connected to the key lock cylinder. The wiring harness from the switch plugs into the lock cylinder assembly, providing the electrical connections based on the key position. The diagram shows the specific pins and their functions (e.g., Start, Run, Accessory, Lock).

Scientific Explanation: The Circuit in Action The 1968 Mustang ignition switch wiring forms a critical pathway for the electrical energy needed to start the engine and generate spark. Here's a simplified breakdown of the key circuits:

• Starting Circuit: Battery Positive (+) -> Ignition Switch "B+" -> Ignition Switch "IGN" -> Ignition Switch "ST" (via contacts) -> Starter Solenoid Coil -> Battery Positive (+) -> Starter Motor. When the key is turned to "Start", the switch contacts close the circuit between "IGN" and "ST", allowing current to flow through the starter solenoid coil. This energizes the coil, creating a magnetic field that pulls the solenoid plunger, which simultaneously closes the high-current circuit between the battery positive and the "S" terminal on the solenoid. This high current flows through the heavy gauge cable to the starter motor, causing it to crank the engine.
• Running Circuit: Battery Positive (+) -> Ignition Switch "B+" -> Ignition Switch "IGN" -> Ignition Switch "BAT" (or directly to coil "I") -> Ignition Coil Primary Circuit -> Ignition Coil "I" -> Ignition Switch "IGN" (via contacts) -> Distributor "R" (Rocker Arm). Once the engine is running, the ignition switch contacts close the circuit between "IGN" and "BAT" (or "I"), allowing current to flow through the ignition coil's primary circuit. This current creates a changing magnetic field in the coil, inducing high voltage in the secondary circuit. This high voltage is routed to the distributor "R" terminal, then through the distributor cap, rotor, and finally to the spark plugs, igniting the air-fuel mixture in the cylinders.
• Accessory Circuit: Battery Positive (+) -> Ignition Switch "B+" -> Ignition Switch "ACC" (via contacts) -> Fuse Panel / Accessories. When the key is in the "Accessory" position, the switch contacts close the circuit between "ACC" and "B+", allowing current to flow to the fuse panel and power accessories like the radio and dash lights.
• Key Position Sensing: The wiring diagram shows how the key lock cylinder's position determines which terminals on the switch are connected. For example, in the "Lock" position, the switch may isolate the "IGN" terminal, preventing any current flow. In the "Run" position, it connects "IGN" to "BAT" and "ACC".

FAQ: Common Questions About the 1968 Mustang Ignition Switch Wiring

FAQ: Common Questions About the 1968 Mustang Ignition Switch Wiring

• Q: What happens if the ignition switch fails? A: A faulty ignition switch can prevent the engine from starting, or worse, leave the vehicle with no power to any electrical systems. Symptoms can include a lack of power to the starter, inability to turn the key, or intermittent electrical problems.
• Q: Can I bypass the ignition switch? A: While technically possible, bypassing the ignition switch is strongly discouraged. The switch provides crucial safety features, including preventing the starter from engaging unless the vehicle is properly secured. Bypassing it can create a safety hazard and potential damage to the electrical system.
• Q: How do I diagnose a problem with my ignition switch? A: Diagnosing ignition switch problems often requires a multimeter and a good understanding of electrical circuits. Start by checking for voltage at the switch terminals in different key positions. A wiring diagram is essential for tracing the circuits. If you are not comfortable working with electrical systems, it's best to consult a qualified mechanic.
• Q: Where can I find a replacement ignition switch? A: Replacement ignition switches can be found at most auto parts stores and online retailers specializing in classic car parts. Ensure you obtain a switch specifically designed for a 1968 Mustang to ensure proper fit and function.

Maintenance and Troubleshooting Tips

Regularly inspecting the ignition switch and its wiring for signs of corrosion, damage, or loose connections can prevent future problems. Applying dielectric grease to electrical connections can also help to prevent corrosion and ensure reliable operation. If you experience intermittent starting problems or other electrical issues, it's a good idea to have the ignition switch inspected by a professional.

Conclusion:

Understanding the wiring of the 1968 Mustang ignition switch is fundamental to maintaining and repairing this iconic vehicle. This intricate system orchestrates the flow of electrical power, enabling the engine to start, run, and power essential accessories. By comprehending the individual circuits and their functions, owners can effectively diagnose and address electrical issues, ensuring their classic Mustang remains a reliable and enjoyable ride for years to come. While the technology has evolved significantly in modern vehicles, the principles of ignition switch operation remain relevant and highlight the ingenuity of automotive electrical engineering from the 1960s. Proper care, regular inspection, and a basic understanding of the system will help preserve the functionality and longevity of this critical component.