LED Turn Signal Indicator Diode | Vintage Honda Motorcycles
If you have converted your gauge-cluster turn signal indicator bulb to LED and the dash light stopped working, this diode is the fix. It prevents electrical cross-talk between the left and right turn signal circuits so your LED indicator flashes correctly.
Why You Need This
From the factory, Honda used a single incandescent bulb in the gauge cluster tied into both the left and right turn signal circuits. That worked because incandescent bulbs are not polarity-sensitive — current can flow either direction. LEDs are polarity-sensitive, so swapping the indicator bulb to LED can leave the dash indicator inoperative or cause both sides to light at once. This diode isolates the two circuits so the LED indicator flashes only on the active side.
Important: This diode must be used with a low-threshold / LED-compatible flasher relay. The OEM thermal flasher often will not trigger reliably with LED loads.
Specifications
| Fits Models | CB175 / CL175 / SL175, CB200 / CL200, CB350 / CL350 / SL350, CB360 / CL360 / CJ360, CB450 / CL450, CB500T, CB350F, CB400F*, CB500K*, CB550*, CB750* |
|---|
| Qty | Sold Individually |
|---|
*Note on fours: The CB350F, CB400F, CB500K, CB550, and CB750 are included in the fitment chart, but later models in these families switched to separate left and right indicator lights. If your bike already has two separate turn signal indicators in the gauge cluster, you do not need this diode.
Installation
Difficulty: Intermediate
Install the diode inside the headlight bucket where the turn signal wiring junctions are located.
- Locate the orange (left turn) and light blue (right turn) wire groups in the headlight bucket.
- Find the gauge-cluster sub-harness — a small bundle running up to the gauges that includes an orange and a light blue wire going to the indicator bulb socket.
- Unplug the orange gauge indicator wire from the main orange turn signal junction. Unplug the light blue gauge indicator wire from the main light blue junction.
- Plug the diode's two red male leads into those main junctions (one red to orange, one red to light blue — either red lead can go to either side).
- Connect one of the gauge indicator wires to the diode's blue female terminal. Connect the other gauge indicator wire to a known-good green/dark green ground in the bucket.
- Turn the key on and test both turn signals. If the dash LED does not flash, swap which gauge wire is on the blue lead vs. ground — there is a 50/50 chance of getting it right on the first try since incandescent bulbs are not polarity-sensitive.
Why the swap test? Incandescent bulbs work regardless of current direction, so the factory may have wired the indicator socket either way. An LED requires correct polarity — one wire must feed through the diode, the other must be ground. If it does not work on the first try, swapping the two wires will fix it.
For the full step-by-step procedure with troubleshooting, see our LED Diode Wiring Guide in the Knowledge Base.
Frequently Asked Questions
Do I need this diode if my external turn signals are LED?
Not necessarily. This diode is specifically for the single turn signal indicator bulb in the gauge cluster when that indicator is converted to LED. Your external turn signals can be LED or incandescent — the diode's job is only to make the dash indicator LED work correctly.
Do I need this if I keep an incandescent indicator bulb in the gauge?
No. Incandescent indicator bulbs are not polarity-sensitive and work with the original single-indicator circuit design without any modifications.
My bike has two separate turn signal indicator lights. Do I need this?
No. This diode is only needed on models with a single shared indicator bulb for both left and right turn signals. Later CB400F, CB550, and CB750 models with separate left and right indicators do not need it.
The indicator lights but does not flash. What is wrong?
This typically points to the flasher relay. Make sure you are using an LED-compatible flasher relay — the OEM thermal flasher often will not trigger with the low current draw of LED bulbs.
You Might Also Need
Last updated: March 2026
