GMC Sierra Parking Light Bulb Size

Additional Notes

• The T20 wedge form factor is the most frequently specified bulb type across these GMC Sierra parking light applications, appearing in multiple variants including the 7443, 7440NA, 7443NA, and 7444NA. All T20 bulbs in these specifications operate at 12V.
• The 7443 is a dual-filament T20 wedge bulb rated at 21W/5W with clear glass, conforming to ANSI standards for the US and Canadian markets. It is the single most widely specified bulb across these Sierra parking light rows.
• The "NA" suffix found on bulbs such as the 7440NA, 7443NA, 7444NA, 4157NA, and 3157NA denotes natural amber glass, meaning the amber color is produced by the glass itself rather than a coating or lens filter.
• The 5702AK, specified for the GMC Sierra 1500 in 2007 and all trims in 2008, is a Sylvania-specific part number for an amber-coated variant of the ANSI 3157 bulb. Its amber color comes from a coating applied to the glass rather than from the glass composition itself, distinguishing it from the NA-suffix bulbs.
• The T25 wedge form factor is shared by the 4157NA, 5702AK, and 3157NA bulbs. All three are dual-filament types rated at 12V, 27W/7W, making them physically and electrically similar despite carrying different part numbers.
• The 7440NA is a single-filament T20 bulb, unlike the other T20 variants in these specifications. Its single-filament design means it serves only one lighting function, whereas dual-filament bulbs such as the 7443 and 7443NA can serve two simultaneously.
• The 7443NA and 7444NA share identical electrical ratings of 12V, 21W/5W and both feature natural amber glass in a dual-filament T20 form. Despite these similarities, they carry distinct ANSI designations and are not listed interchangeably within these specifications.
• For the GMC Sierra 3500 HD in 2014, the specified bulb is the 4157NA, a T25 dual-filament type, while the 1500 trim for the same year uses the 7443, a T20 dual-filament type. These two bulbs differ in both physical size and wattage, making them non-interchangeable between trims.
• The 2018 Sierra 1500 with HID headlamps uses the 7440NA, a single-filament natural amber T20 bulb, while the 2017 Sierra 1500 with HID headlamps uses the 7440NA for one application and the 7443NA, a dual-filament natural amber T20, for another. The HID headlamp condition is a noted fitment qualifier in both years.
• The 3157NA was the specified front parking light bulb for the GMC Sierra across the 1999-2006 model years, representing the longest continuous span of a single bulb type in these specifications.