The Isuzu Impulse front and rear turn signal bulbs utilize 1157 size specifications, with rear applications also accommodating 1157, P21W, and 1073 bulb sizes. The replacement chart covers 1983 through 1992 production years with corresponding bulb size data.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 1157 bulb is the most frequently specified type across the Isuzu Impulse turn signal data, appearing in all front turn signal positions for model years 1983-1992 and in all rear turn signal positions for 1988-1992.
The 1157 is a dual-filament bulb operating at 12V with a 21W main filament and a 5W secondary filament, mounted on a BAY15d bayonet base. Its dual-filament design allows a single bulb to serve both turn signal and parking light functions in the same housing.
The BAY15d base used by the 1157 features two offset pins at different heights, which physically prevents incorrect insertion and distinguishes it from single-filament bayonet bases.
The rear turn signal on the Isuzu Impulse for 1983 and 1985 uses the 1073 bulb, a single-filament ANSI-standard type rated at 12V and 13W with a BA15s bayonet base.
The 1073 is considered a lower-wattage variant of the 1156 bulb. Both share the BA15s base, but their wattage ratings differ, which affects light output and may affect compatibility with flasher relay timing.
The rear turn signal for model years 1984, 1986, and 1987 uses the P21W bulb, an ECE-standard single-filament type rated at 12V and 21W with a BA15s bayonet base.
Although the P21W and 1073 share the same BA15s bayonet base, their wattage ratings differ significantly at 21W versus 13W. This difference means the two bulb types are not interchangeable without potential effects on flasher relay operation.
The front and rear turn signal positions on the Isuzu Impulse do not share a consistent bulb type across all model years. The front position uses the 1157 throughout 1983-1992, while the rear position varies across three different bulb types depending on the year.
The 1157 and the P21W both operate at 21W for their primary filament and share a similar light output level for signalling purposes, but their base types differ. The 1157 uses a BAY15d base and the P21W uses a BA15s base, making them physically non-interchangeable.
The rear turn signal specification for the Isuzu Impulse transitions from the 1073 in 1983 to P21W in 1984, back to 1073 in 1985, then P21W again in 1986-1987, before shifting to the 1157 from 1988 onward.