Pontiac Grand LeMans front turn signal bulbs use 1034NA or 1157NA size, while rear turn signal bulbs use 1156 or 1157 size. The replacement chart covers 1975 through 1981 production years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 1157 and 1157NA are both dual-filament bulbs rated at 12V and 21W/5W with a BAY15d bayonet base. The 1157NA is a variant of the 1157 distinguished by its natural amber glass, which produces the amber signal color without relying on a tinted lens.
The 1034NA shares the same BAY15d bayonet base and 12V/21W/5W dual-filament configuration as the 1157 and 1157NA, making it a close relative within the same bulb family. Its natural amber glass also eliminates the need for an amber-colored housing or lens to produce a compliant turn signal color.
The 1156 is a single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base. Because it has only one filament, it operates solely as an on/off signal source rather than serving a combined turn-and-parking-light function.
The BAY15d base used by the 1034NA, 1157NA, and 1157 is not interchangeable with the BA15s base used by the 1156. The two base types differ in their pin offset configuration, and substituting one for the other is not physically possible without modification.
For the Pontiac Grand LeMans front turn signal, the 1034NA was specified for 1975, 1977, and 1981, while the 1157NA was specified for 1976, 1978-1980. Both bulb types share the same base and wattage ratings, but only the application year determines which is correct for a given vehicle.
The rear turn signal of the Grand LeMans used the dual-filament 1157 for 1975-1977 and 1979, while the single-filament 1156 was specified for 1978 and 1980-1981. The shift between these two bulb types across model years reflects a change in the rear lamp circuit design, as the 1156 and 1157 are not interchangeable due to differing base types and filament counts.
The 1157 and 1034NA are both variants within the same dual-filament family and share the BAY15d base, but the 1034NA's amber glass coating makes it a distinct part number. Using a clear-glass 1157 in a position specified for the 1034NA may affect the color output of the turn signal if the lens itself is also clear.
All four bulb types referenced in these specifications conform to ANSI standards applicable in both the United States and Canada, indicating they meet the same regulatory baseline for automotive lighting in both markets.