Which Filament in Optronics Bulb # A1157B is Used for the Turn Signal

Updated 09/09/2013 | Published 09/05/2013

Question:

Which filament on a 1157 bulb is used for the turn signal

asked by: Pat W

Expert Reply:

The Optronics 1157 Replacement Bulb, part # A1157B, and similar dual-filament bulbs have two different filaments. One filament is of a different resistance value, and thus makes a brighter light. That is why one bayonet on the bulb casing is at a different position than the other bayonet - so that you dont install the bulb the wrong way. The basic filament usually on the brown wire is running lights, the other filament usually green or yellow depending on which side of trailer has different resistance value, making it brighter, and used for braking/turn signal.

expert reply by: Adam R