SW1951C Heavy Duty Starter Solenoid Relay

Key Features

• High-Current Copper Terminals: Equipped with premium copper contact studs that ensure maximum electrical conductivity and minimal voltage drop during high-amp cold starts.
• Heavy-Duty Solenoid Coil: Features an upgraded internal winding designed to operate reliably under extreme under-hood temperatures and high-vibration off-road conditions.
• Phenolic Molded Housing: Constructed from high-temperature phenolic plastic to resist cracking, moisture intrusion, and electrical tracking between terminals.
• Universal 4-Terminal Interface: Includes two primary battery/starter studs and two small signal terminals (S and I), maintaining the classic Ford electrical layout for easy wiring.
• Direct OE-Spec Fitment: Designed with the standard vertical mounting bracket and hole spacing found on Ford trucks and cars from the 1980s through the early 2000s.

Replaces / Cross-Reference Part Numbers

• Ford: E5TZ-11450-A, E7TZ-11450-A, E9TZ-11450-B, F5TU-11450-BA
• Motorcraft: SW1951, SW1951A, SW1951C
• Other: 6012928, B6AZ-11450-A, F1491, SS581

Compatibility & Fitment

This solenoid is the "classic" fender-mounted relay used across decades of Ford, Lincoln, and Mercury vehicles. Key compatible models include:

• Ford F-Series: F-150, F-250, F-350, F-450, F-550 (including Super Duty models up to the early 2000s).
• Ford Trucks & SUVs: Ranger, Bronco, Explorer, Expedition, Excursion.
• Ford Vans: E-150, E-250, E-350, E-450 Econoline series.
• Ford Cars: Mustang, Crown Victoria, Escort, Taurus, Thunderbird.
• Lincoln & Mercury: Town Car, Grand Marquis, Navigator, Mountaineer.

When to Replace

• The "Clicking" Sound: You hear a single, sharp click when turning the key, but the starter motor does not engage.
• Intermittent Starting: The vehicle starts fine one moment but refuses to turn over the next, often requiring a "tap" on the solenoid to work.
• Starter Stays Engaged: The starter motor continues to spin even after the engine has started and the key is released (indicates the internal contacts have "welded" shut).
• No Sound at All: Turning the key results in total silence, suggesting the internal solenoid coil has failed or is not receiving the signal.
• Corroded Terminals: The copper studs have become heavily oxidized or the mounting bracket is rusted, preventing a solid ground connection to the fender.

Installation Tips

• Battery Disconnect: Always disconnect the Negative (-) battery cable before starting. This solenoid is connected directly to the "hot" side of the battery and can cause a massive short if accidentally grounded.
• Grounding is Key: This relay grounds through its metal mounting bracket. Ensure the fender area where it bolts on is clean and free of paint, rust, or debris to ensure a solid electrical circuit.
• Terminal Orientation: Note the "S" and "I" markings on the small terminals. The "S" terminal (Start) receives power from the ignition switch, while the "I" terminal (Ignition) provides a bypass to the coil during cranking on older points-based systems.
• Avoid Over-tightening: The large copper studs are seated in plastic. Use a back-up wrench if possible to avoid twisting the internal contacts while tightening the main battery cables.
• Safety Check: After installation, ensure all wires are clear of moving parts like the fan or hot exhaust manifolds.