Collection: Classic & Collectible Cars > Signalling & Interior

Vintage Car Lighting: Bayonet Bases

The bayonet base (BA = Bayonet) has been used in car signal lights since the 1920s. It remains very common today — it's even the standard on most modern vehicles for turn signals and brake lights.

On a classic car, you will mainly find:

• BA15S (single contact, symmetrical pins) — single filament 21W or 5W. Used for turn signals (P21W), side lights (R5W) and reverse lights.
• BAY15D (double contact, offset pins) — double filament 21/5W (P21/5W). Combines brake light and tail light in a single bulb. Very common on post-war cars.
• BA15D (double contact, symmetrical pins) — double filament, less common than the BAY15D but present on some European models.

Specific Bases for Vintage Cars: BA20s, BA21d

These rarer bases were used on pre-war and 1950s vehicles. Difficult to find outside of specialists:

• BA20s — 20 mm diameter single-contact bayonet base. Used on certain popular vintage cars, microcars, and old industrial equipment.
• BA21d — 21 mm double-contact bayonet base. Found on specific European models from before 1960.

These formats are not interchangeable with the modern BA15S — the difference in diameter prevents any cross-fitting. Pharos Boutique maintains these references specifically for classic vehicle enthusiasts and restoration workshops.

Classic Car Interior

The interior lighting of a vintage car uses the same principles as a modern vehicle, but often with specific bases:

• Ceiling light — often festoon or BA9s
• Dashboard and indicator lights — BA7S, T4W, BA9s bases depending on the model
• Glove box lighting — generally W5W or BA9s

Voltage: 6V or 12V?

Pay attention to your vehicle's voltage — most cars from before 1960 operate on 6 volts, and only 6V bulbs are suitable (Citroën Traction, first generation 2CV, Renault 4CV, Peugeot 203/403, Simca Aronde). For vehicles after 1960, check the manufacturer's plate or the battery. See also our complete 6V range.

Identify your bulb base

Remove the faulty bulb: the type, wattage (W), and voltage (V) are engraved on the base or the glass. For old bulbs with worn markings, compare the dimensions with our catalog or contact us with the vehicle's make/model/year — we can easily identify the reference.