The Mazda RX-4 front and rear side marker bulbs both utilize an 89 size bulb configuration. The replacement chart covers 1974 through 1978 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 Mazda RX-4 uses the 89 bulb for both front and rear side marker positions across the 1974-1978 model years.
The 89 is an ANSI-standardized bulb type, meaning its physical and electrical specifications are governed by a recognized North American industry standard applicable in both the United States and Canada.
The 89 bulb operates on a 12-volt electrical system and draws 13 watts, placing it in the lower-power range of the BA15s bayonet bulb family.
The 89 uses a BA15s bayonet base, which is a single-contact base type. The "s" in BA15s denotes a single center contact at the base, as opposed to the dual-contact BA15d configuration.
The 89 is a single-filament bulb, meaning it serves one lighting function only, consistent with its use in side marker applications rather than combined stop/tail positions.
The 89 is described as a lower wattage variant of the 1156. Both share the BA15s bayonet base, but the 1156 operates at a higher wattage, making the two types electrically incompatible as direct replacements despite their physical similarities.
Because the 89 and 1156 share the same BA15s base, the 89 socket will physically accept a 1156 bulb, but the wattage difference means substitution can affect circuit load and potentially damage associated components.
The front and rear side marker positions on the RX-4 use the same bulb size for all covered model years, indicating a uniform socket specification across both locations throughout the vehicle's production run in this period.