JST-SM and LED String Connectors
If you've bought an addressable LED string, LED pixels, a strip with a pigtail, or almost any prewired low-voltage lighting harness, you've met this connector: a small inline wire-to-wire connector, usually 2-, 3-, or 4-pin, that marketplaces call JST-SM, SM, "LED connector," "2/3/4-pin LED connector," or just "JST-style."
It deserves its own page because it is everywhere in LED work — and because almost everything about it, from the name to the rating, needs verification.
ID marks: an inline pair in the middle of a cable — 2.5 mm pitch, positive latch, no PCB side.
What you're actually looking at
- JST-SM is commonly seen as an inline wire-to-wire family/style in hobby LED wiring — one half on the string, the pigtail half on your controller.
- The genuine JST SM series is documented: 2.5 mm pitch, disconnectable crimp wire-to-wire, 3 A AC/DC max (2 A for the 18-circuit version), 250 V, wire range AWG #28–22, per the official JST datasheet.1 But clone and "compatible-style" parts circulate freely in LED listings and are not covered by those numbers — latch engagement, contact fit, and dimensions can differ. Verify pitch, latch geometry, housing shape, contact style, wire gauge, and pin count against a drawing, not the product title.
- Many LED pigtails are sold pre-crimped/prewired. This is usually the sane choice — buying matching prewired pigtail pairs beats hand-crimping small wire-to-wire contacts. See Crimping.
- Verify polarity and pinout every time. LED conventions like power/data/ground are common, but wire colors and pin order are not guaranteed — red is not always positive, and data direction matters on addressable strings (they have an input end and an output end).
- Do not assume waterproofing. An outdoor-rated LED product does not make its little inline connector sealed — many are open connectors heat-shrunk or left bare. Sealing, if any, has a stated condition.
- Do not assume a current rating from appearance or product title. "LED connector" is not a rating.
The small inline connector that came on an LED string may be fine for that string, but that does not automatically make it appropriate for power injection, longer runs, outdoor exposure, or higher-current loads. Calculate current and choose the connector/wire system intentionally.
Power injection is a different job
Addressable LED runs of any length need power injected in parallel — and that current does not belong on the little data-string connector. For power injection and supply wiring, use appropriately rated hardware chosen on purpose: rated power connectors, distribution blocks, ferrules into screw terminals, Wago-style lever connectors, or XT-class connectors as appropriate — sized against the calculated LED current and verified against the part's documentation, not its title. The engineering track's power vs signal thinking and high-current DC path apply the moment real amps show up.
Before using JST-SM-style connectors in an LED project
- Pin count
- Pitch / series (measured, not assumed)
- Genuine vs clone / unknown
- Wire gauge
- Current per pin (genuine JST SM: per the datasheet1; unknown/clone parts: treat as unrated until verified)
- Total LED current (calculated, worst-case white)
- Voltage
- Polarity (verified against the controller, not wire color)
- Data direction, if addressable LEDs
- Indoor/outdoor exposure
- Strain relief
- Waterproofing/sealing condition (mated? heat-shrunk? none?)
- Mating cycle expectation
- Prewired lead source (so you can buy the same one again)
- Spare mating pairs available
Related: JST Is Not One Connector · Power vs Signal Connectors · Buying the Right Mating Parts.