The GMC PM250 front turn signal requires bulb sizes 1034, 1073, or 1129, while the rear turn signal uses either 1073 or 1129 bulb size. The replacement chart covers 1955 through 1957 vehicle 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 GMC PM250 front turn signal uses three different bulb sizes across the 1955-1957 model years, while the rear turn signal uses only two distinct bulb sizes across the same span.
The 1034 and 1129 bulbs share identical electrical ratings of 12V and 21/5W, and both use a BAY15d bayonet base with dual filaments, making them variants of the 1157 bulb type under the ANSI standard.
A dual-filament bulb, such as the 1034 and 1129, carries two separate filaments within a single envelope, allowing one circuit to handle turn signaling and another to handle a secondary function such as running or brake light duty.
The 1073 bulb is a single-filament type rated at 12V and 13W, fitted with a BA15s bayonet base, and is classified as a lower wattage variant of the 1156 under the ANSI standard.
The BA15s base of the 1073 and the BAY15d base of the 1034 and 1129 are physically distinct. The BAY15d base features offset pins to prevent incorrect installation of a dual-filament bulb in a single-filament socket, so these bulb types are not interchangeable.
The GMC PM250 (1955) uses the 1129 bulb for both the front and rear turn signals, making it the only model year in these specifications where both positions share the same bulb size.
The 1957 GMC PM250 front turn signal uses the 1034 bulb, while the rear uses the 1073, meaning the two positions require different base types and filament configurations in that model year.
All three bulb types listed in these specifications conform to ANSI standards applicable in both the United States and Canada.