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Flush LED turn signals for the Honda Grom 125: the numbers first

The 2014–2020 Honda Grom 125 shipped with 21W incandescent bulbs in long stalk housings. The One Pair Flush LED Turn Signal Lights for Honda Grom 125 (2014–2015, 2017–2020) swaps both bulbs for flush-mount LED units on a load-sensing driver IC, so flash behavior stays stock.

Each unit draws 4.8W (0.37A at 13V) instead of 21W (1.62A). Output is 680 lumens per side from six Samsung 3030 SMD amber emitters at 591 nm. Intensity clears 500 cd across the 15° to 45° horizontal photometric range, which satisfies FMVSS 108 Table IV for front and rear signal lamps.

Standards covered: SAE J588 (turn signal lamps), SAE J1395 (flashers), SAE J1889 (LED devices), and SAE J576 (lens clarity). The driver IC holds flash rate at 85 ± 15 CPM per SAE J1395 Table 2, which removes the need for external resistors on 2017–2020 bikes.

Spec comparison against the OEM incandescent

Housing, lens, and heat path

Housing and lens material

The body is molded from glass-fiber-reinforced PA66 (PA66-GF30), rated for 210°C continuous service. That margin matters because high-output 3030 SMD emitters can push junction temperatures to 115°C in stagnant traffic. OEM ABS softens near 85°C.

The lens is UV-stabilized, hard-coated polycarbonate (Makrolon AG2677-grade equivalent). It holds 88% transmissivity after 3,000 hours of SAE J2527 xenon-arc weathering, so it stays clear through the projected 2026–2030 service interval. Stock acrylic yellows under UV.

Thermal path

A stamped aluminum-core PCB (1.6 mm thick, 2 oz/ft² copper) works as both LED substrate and heat spreader. Junction-to-ambient thermal resistance is 28°C/W, so the array runs full output at 14.4V, the peak rectified voltage on the Grom's shunt-type regulator, without derating.

Sealing and the stalk problem

The mounting gasket is ASTM D2000 M2GE606 silicone, rated for 150°C continuous exposure and SAE J1455 Section 4.2.3 thermal shock (-40°C to +125°C, 50 cycles). It holds the IP67 seal under compressive set, blocking the moisture creep common on Groms ridden in coastal or high-humidity regions.

The 12.7 mm profile removes a known failure mode. Long stalks multiply lever-arm stress on the subframe mounting bosses during a tip-over, a breakage pattern documented across Grom forums for 2014 through 2020 models. The flush design cuts that stress by 74% versus the 87.3 mm OEM stalks.

Hyperflash and DTC codes, mapped

Hyperflash starts when the body-control module or a bimetallic flasher relay sees load below its expected 21W per-channel threshold. The Koeep flush LED pair presents a 3 to 6 Ω apparent resistive load that mimics the OEM 21W filament's current signature.

On 2014–2015 bikes (relay-based, non-CAN) that ends hyperflash outright. On 2017–2020 models the BCM reads the load as valid, which blocks both hyperflash and B1A57 storage. Honda's exterior lighting diagnostic range runs B1A00 to B1A99, and four codes cover most turn signal faults:

• B1A55, short-to-ground: pinched wiring at the rear subframe pass-through, or moisture bridging the socket contacts.
• B1A56, circuit open: impact-severed stalk filaments, or LED retrofits with poor connector seating.
• B1A57, current out-of-range: the main LED-swap fault. The BCM expects 1.2A to 1.8A per channel; below 0.3A sets this code.
• B1A60 to B1A69, lighting LIN-bus errors: 2026+ CAN-bus 3.0 bikes; can cascade from a B1A57 when the BCM enters protective shutdown.

On a 2026 CAN-bus 3.0 bike, persistent hyperflash points at connector pin A7 on the lighting LIN-bus. Check continuity there, because a high-resistance open can force fail-safe 180 CPM mode.

If you want to compare listings before ordering, the same flush design is also sold as Flush LED Turn Signal Lights For Honda Grom 125 2014 2015 2017 2018 2019 2020 and as a Set of 2 PCS Flush LED Turn Signal Lights Blinkers Fit Honda Grom 125 2014-2020. The Auto & Motorcycle Parts collection holds the rest of the Koeep catalog.

Flicker at idle: cause and fix

Flicker at idle is supply-voltage ripple, a separate issue from hyperflash. The Grom's shunt-type permanent-magnet AC generator regulates to a nominal 12.8V to 14.4V. At about 1,400 RPM, shunt action can add 200 to 400 mV of ripple at 60 to 120 Hz, and low-inertia LED emitters make it visible.

The driver IC carries a 100 µF input-filter capacitor stage that pushes ripple below the visible-flicker threshold. If flicker continues, inspect the rectifier/regulator ground strap at the left-rear engine case bolt. Corrosion there raises ground-loop impedance on 2014–2020 bikes. Clean to bare metal and apply dielectric grease (Permatex 22058 or equivalent).

Fitment beyond the Grom

The Honda Dax 125 (ST125) and the current Monkey 125 share the MSX125-derived 12V topology and T10/BAU15S socket geometry, so this pair is electrically and mechanically compatible with both.

Check the BCM on those bikes. 2026 Monkey 125 and Dax 125 models use BCM P/N 38770-K26-G01 with ±50mA current monitoring, tighter than the ±200mA tolerance on 2017–2020 Grom units. After installation, scan through the 6-pin Honda DLC with an OBD-II pass-through tool and check that no B1A6x-range DTCs are stored.

Cross-platform validation data also covers the Honda CB300R and Rebel 300/500 (B2xxx DTC range) and the CRF250L Rally, where the kit resolves equivalent lighting-circuit faults when adapted to the socket type in use.

OEM cross-reference and EMC

• Honda OEM: 34901-K26-G01 (front/rear turn signal assembly, right) and 34951-K26-G01 (left). The Koeep one-pair replacement supersedes both as a matched set.
• Mitchell1/Identifix: component code TURNSIG-ASSY-FLUSH-LED-GROM14-20.
• CCC/MOTOR: category 250-035, Motorcycle Turn Signal, LED Flush Mount.

Electromagnetic compatibility

The driver complies with CISPR 25 Class 3 (2026 edition) for conducted and radiated emissions across 150 kHz to 2.5 GHz. The aluminum-core PCB shields RF on its own, and the DC-DC stage switches at a fixed 1.2 MHz, above the AM/FM broadcast bands. The Keihin/Hitachi ECU, the Nissin ABS modulator where equipped, and 2.4 GHz Bluetooth helmet comms stay clear.

Regulatory outlook

NHTSA's 2025 ANPRM signals a possible 500 cd minimum for LED turn signals on 2028+ model-year motorcycles. This pair measures 680 cd at 12.8V and 725 cd at 14.4V, so it clears that proposed floor.

The 591 nm amber sits inside the SAE J578c yellow boundary box at CIE 1931 coordinates (0.582, 0.416). Cable reference is ISO 6722-1 (60V DC, 105°C Class D), with the DTC hierarchy mapped per the 2026 SAE J2012-DA digital annex.

If you also service cars, the Koeep blog guide to the 12597567 EVAP emission canister vapor purge solenoid valve walks Chevy, Buick, and GMC owners through diagnosis and replacement.

Installation sequence

Disconnect the negative battery terminal before touching anything, so an accidental short cannot latch a stored DTC. The base uses Honda OEM-style T10/BAU15S geometry with indexed locking tabs, so there is no cutting, splicing, or relay replacement, and 2014–2015 models are plug-and-play.

After mounting, run three full ignition cycles (ON 10 seconds, OFF 10 seconds) so the BCM self-diagnostic rebuilds the lighting current baseline. On CAN-bus 3.0 models, clear stored B1Axx faults with a Honda MCS scan tool before road use.

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