Motorcycle headlight bulb bases: P15D vs H4 vs BA20D
Short answer
Do not choose a headlight bulb by name alone: "H6" is used for two different bases. Take out the old bulb and check its base shape and the code stamped on it. Many scooters and underbones use P15D-25-1 (also sold as M5 or H6) [2][3]; many sport bikes use H4 (base P43t) or HS1 (PX43t) [1][2]. These bases do not swap. Before fitting an LED, check whether your headlight runs on DC from the battery or on AC straight from the stator, because AC is a common cause of LED flicker and failure [4].
Common headlight bulb bases
| Name you see | Base | How it fits | Typical bikes |
|---|---|---|---|
| M5 / H6 / P15D | P15d-25-1 | Flange base, pushes straight in and is held by a clip | Many scooters and underbones [2] |
| H6 (other meaning) / S2 | BA20d | Bayonet with two pins at the same height; twist to lock | Older and some small motorcycles; not interchangeable with P15D [1] |
| H4 | P43t | Large flange with three flat terminals | Many sport and naked bikes [1][2] |
| HS1 | PX43t | Looks like H4, different flange | Some sport and mid-size motorcycles [2] |
Model lists in [2] come from the Indonesian market; the same model name can use a different bulb in other countries or years. Always confirm with the old bulb or the owner's manual.
How to identify your bulb in 3 steps
- Look at the shape. Flange that pushes in, or bayonet pins that twist? Two terminals or three?
- Read the code. The metal base is usually stamped, for example "P15d-25-1" or "P43t".
- Then pick color and features. Only after the base matches should you compare light color, high/low beam and size.
Why an LED headlight flickers or does not light
- AC lighting. On some small bikes the headlight is fed alternating current directly from the stator. The voltage rises with engine speed, and a failing regulator can push it higher. An LED needs DC or a built-in driver that can handle AC [4]. With the engine running, measure the headlight plug with a multimeter on DC and AC before buying; with the engine off, an AC system may show no voltage at all.
- High and low beam swapped or only one works. The pins of a dual-beam bulb must match the bike's high, low and ground wires. Confirm with a multimeter instead of trusting wire colors.
- No space behind the lamp. LED bulbs have a heat sink behind the base. Check there is room inside the headlight housing and that the dust cover still fits.
- Beam pattern. The housing was designed for a filament. Before changing the bulb, park facing a wall a few metres away and mark the top edge of the original beam. After fitting, make sure the new beam is not above that mark.
Fitting a P15D bulb
- Lights off and let the old bulb cool.
- Unplug the connector and remove the rubber dust cover.
- Release the retaining clip and take out the old bulb.
- Line up the flange of the new bulb with the slots, push it in and refit the clip.
- Refit the cover and connector, then test low beam and high beam before riding.
Our headlight bulb
P15D-25-1 LED headlight bulb, 12V
Projector lens with high and low beam. Two versions: white + yellow (low beam white, high beam yellow) and white + white. Rated 12V; AC compatibility is not confirmed, so check your headlight circuit (see above) before ordering.
Buy on TikTok ShopSources
- Wikipedia, List of automotive light bulb types (H4 = P43t, HS1 = PX43t, S2 = BA20d): en.wikipedia.org
- Gridoto, motorcycle bulb substitutes by socket type (Indonesia): gridoto.com
- Philips Philippines, M5 moto headlight bulb product page: philips.com.ph
- Detik Oto, LED headlight and motorcycle electrics (Indonesia): oto.detik.com
General guidance only. Check your owner's manual and local rules on headlight color and aiming.