Product Specifications

I. Overview & Historical Significance
        The 9004 (P29t) is a historic and widely used dual-filament halogen bulb that served as the standard for combined high/low beam headlights in a vast number of North American, Japanese, and Korean vehicles from the 1980s through the early 2000s. Its three-tab P29t base design became synonymous with the "sealed beam replacement" era, offering improved performance over older sealed-beam units.

II. Key Characteristics & Function

1. Dual-Filament Design: Integrates separate filaments for low beam (typically 45W) and high beam (typically 65W) within a single bulb. A three-terminal base allows independent control of each function.

2. Regulatory Beam Pattern: The precise positioning of the two filaments and the P29t base's fixed orientation ensure the bulb creates a proper SAE/DOT-compliant beam pattern when installed in its designated headlamp housing.

3. Universal Legacy Application: It was the go-to bulb for most non-H4 composite headlights during its peak, found in countless sedans, trucks, and SUVs.

III. Identification & Compatibility

• Base: P29t. This is a plastic three-tab bayonet base with tabs of differing sizes to prevent incorrect installation. It is the defining feature of the 9004 bulb.

• Critical Distinction from H4: The 9004 (P29t) is the North American standard for dual-beam bulbs. It is NOT interchangeable with the similar but different European/International H4 (P43t base), which has a metal three-prong base.

• Interchangeability Note: In some older systems, the 9004 may have been superseded by or interchangeable with the 9007 bulb, but this is vehicle-specific. Always verify against the original.

IV. Important Application & Handling Notes

• Primary Use: For composite headlamp units (replaceable-bulb type) using a single bulb for both high and low beams.

• Installation Caution: The three-tab base must be aligned correctly with the socket. Forcing it can damage the tabs or socket.

• No-Touch Rule: Handle the bulb by its plastic base only. Contaminants from skin oils on the glass can cause hot spots and premature failure.

• Electrical Check: Ensure all three contacts in the headlamp socket are clean and making proper connection.