Ford Aerostar Turn Signal Bulb Size

Additional Notes

• The Ford Aerostar front turn signal specifications span the 1986-1997 model years and reference six distinct bulb types: 1157, 1157NA, 1034NA, 2357, 3157, and 3157NA. All are dual-filament designs operating at 12 volts.
• The 1157 and its variants (1157NA, 1034NA, 2357) share the BAY15d bayonet base, which uses two offset pins at different heights to ensure correct orientation during installation. Despite this shared base, the filament wattages differ across these types, making them non-identical substitutes.
• The 1034NA is described as a variant of the 1157NA, both carrying natural amber glass and a BAY15d base. However, the 1034NA is rated at 21W/5W while the 1157NA is rated at 21W/5W as well, with the distinction lying in their ANSI classification rather than wattage output.
• The 2357 bulb, used in the front turn signal position for the 1990-1991 Ford Aerostar, is rated at 26.9W/8W, making its high-beam filament notably brighter than the 1157 at 21W/5W, despite sharing the same BAY15d bayonet base form factor.
• The 3157 and 3157NA are T25 wedge-type bulbs rated at 27W/7W. The NA designation on the 3157NA indicates natural amber glass, meaning the amber color is produced by the glass envelope itself rather than by an amber-tinted housing or lens.
• The rear turn signal specifications introduce three additional bulb types not present in the front: 3156, 3457, and 2456. The 3156 is a single-filament T25 wedge bulb at 27W, while the 3457 is a dual-filament T25 wedge at 27W/7W, meaning these two types are not interchangeable despite sharing the same wedge base form.
• The 2456 is classified as a festoon bulb for specialty applications, a cylindrical form factor held in place by spring-loaded end caps rather than a bayonet or wedge base. This makes it physically incompatible with sockets designed for wedge or bayonet-type bulbs.
• The 1156, used in the rear turn signal position of the 1986 Ford Aerostar, carries a BA15s single-contact bayonet base and is rated at 21W. It is not interchangeable with the BAY15d-based bulbs used in other model years, as the BA15s base has a single pin rather than the dual offset pins of the BAY15d.
• The rear turn signal position of the Ford Aerostar uses a single-filament bulb in several years, including the 3156 and 1156 types, while the front position consistently uses dual-filament bulbs across all listed model years. Single-filament rear bulbs serve only the turn signal function, whereas dual-filament types can serve combined functions such as turn signal and running light simultaneously.
• Across both front and rear positions, the Ford Aerostar specifications show no single bulb type used consistently throughout the entire 1986-1997 production run, reflecting multiple changes in socket and bulb design across model years. Substituting a bulb from a different model year risks a mismatch in base type, filament count, or wattage.