Autolite 405 Spark Plug

Autolite 405 Copper Resistor Spark Plug

Autolite 405 is a copper resistor spark plug built for OE-style fit, form, and function across a range of classic applications. It is specified for quick starts, steady idle quality, and smooth throttle response in vehicles such as Chevrolet El Camino, GMC G1000 Series, Bentley Continental, and Rolls-Royce Silver Dawn.

The Autolite Copper Resistor Spark Plug line focuses on dependable ignition performance at a value-oriented price point. Part number 405 uses a copper center electrode core, nickel tip materials, a ceramic insulator, and a 5,000 ohm resistor to help control electrical noise while maintaining consistent spark delivery.

Key Features

• Autolite 405 copper resistor spark plug for OE-style replacement
• Copper center electrode core with nickel center electrode tip
• Nickel ground electrode tip with tapered design
• 5,000 ohm resistor type for reduced ignition interference
• Pre-gapped to 0.034 in. / 0.90 mm
• 14.0 mm thread diameter, 0.750 in. reach, flat seat
• 13/16 in. hex size with removable nut terminal
• Ceramic short insulator and single ground electrode

Detailed Description

Autolite 405 is a standard copper resistor spark plug engineered for secondary ignition systems that call for OE-style dimensions and performance. The copper core supports efficient heat transfer, while the nickel electrode materials and tapered ground electrode design help maintain stable spark characteristics under normal operating conditions. With a flat seat, 14.0 mm thread diameter, 0.750 in. reach, and 13/16 in. hex, this spark plug matches common vintage and classic engine specifications. It is a direct-fit choice for applications including 1964-1966 Chevrolet El Camino, 1968 Chevrolet El Camino, and 1964-1966 GMC G1000 Series, as well as 1952-1954 Bentley Continental and 1949-1954 Rolls-Royce Silver Dawn. This part cross-references Champion Spark Plug 504 for the same application.

What It Helps Address

• Hard starting caused by worn or fouled spark plugs
• Rough idle from inconsistent ignition output
• Reduced throttle response from weak spark delivery
• Ignition noise concerns in resistor-equipped systems
• Maintenance replacement for OE-style classic vehicle tune-ups

Installation Notes and Tips

Verify the required thread diameter, reach, seat type, and gap before installation. Autolite 405 is pre-gapped at 0.034 in. / 0.90 mm, but the engine specification should always take priority for the application. Use the removable nut terminal only if your ignition lead or boot requires it, and confirm plug wire routing and torque against the vehicle service manual. For classic Chevrolet El Camino, GMC G1000 Series, Bentley Continental, and Rolls-Royce Silver Dawn applications, match the plug to the original OE-style heat range and configuration.

Quality Assurance

Autolite supplies ignition products to the automotive aftermarket and original equipment manufacturers, and this spark plug reflects that OE-style manufacturing approach. The 405 is built to deliver consistent secondary ignition performance with the materials and dimensions expected for direct replacement service.