Triumph Turn Signal Diode Kit for LED Indicators
The British Iron Turn Signal Diode Kit (PN MBI-TSDIODE) fixes the most common problem with fitting LED turn signals to a Triumph: both sides flash at once when you signal left or right. Many Triumphs use one shared incandescent indicator light on the dash. That bulb links the left and right turn signal circuits, and LED signals are so efficient that the small current passing through the bulb is enough to light the other side. The kit adds a pair of diodes that keep the left and right circuits apart, so only the side you select flashes and the dash indicator still lights.
Why LED turn signals make all four indicators flash
An incandescent indicator bulb is just a coil of wire with no polarity. On a bike with a single dash indicator light, one side of that bulb connects to the left turn signal wire and the other side to the right. With the original filament bulbs, the opposite side’s turn signals pull very little current through the dash bulb. LED turn signals need so little current that the power passing through the dash indicator is enough to light them. The result is that all four signals flash, or flash dimly on the wrong side, every time you signal.
The diode kit changes how the dash indicator is wired. Each turn signal wire feeds the indicator through its own diode, and the other side of the indicator goes to ground. A diode lets current flow in only one direction, like a one-way valve, so current from the left side can’t flow back into the right side. Triumphs that left the factory with LED turn signals use a similar diode arrangement in the wiring harness. The Bonneville Shop explains this in detail, with power-flow diagrams, in Using LEDs with Traditional Turn Signal and High Beam Indicator Lights.
Key benefits
- Stops all four turn signals flashing at once after an LED turn signal conversion
- Keeps the dash turn signal indicator working, so you don’t have to remove the bulb
- Isolates the left and right circuits to stop back-feed and voltage drop
- Lets you run brighter, longer-lasting LED turn signals, such as compact mini markers that suit a fender eliminator or a pre-’71 Bonneville look
- Low-cost, small and easy to hide behind the headlight or under the seat
Do you need this diode kit?
- You need it if: your Triumph has one shared incandescent turn signal indicator light on the dash, and you’ve fitted (or plan to fit) LED turn signals.
- You probably don’t need it if: your dash has separate left and right indicator arrows, or your bike came from the factory with LED turn signals. Those harnesses usually already isolate the two circuits.
- Quick test: if signaling one way makes all four LEDs flash, and the problem stops when you remove the dash indicator bulb, the diode kit is the permanent fix.
Diode kit vs. LED flasher relay vs. load resistors
LED conversions can cause two different problems, and each one has its own fix:
- All four signals flash at once: caused by back-feed through a shared incandescent dash indicator. Fix: this diode kit.
- Hyper-flash (signals blink too fast) or signals that don’t flash: caused by a factory flasher relay that expects the heavier current of filament bulbs. Fix: an LED-compatible electronic flasher relay or load resistors. The diode kit doesn’t change the flash rate.
Some bikes have only one of these problems, and some have both. If you replace all four signals with LEDs, plan to check the flash rate too.
Installation overview
- Disconnect the battery.
- Find the turn signal indicator bulb holder in the headlight shell or instrument wiring. Use the wiring diagram in your service manual to identify the left and right turn signal feeds.
- Connect the left and right turn signal wires to the indicator through the diodes, observing the diode direction, so that both diodes feed one terminal of the indicator.
- Connect the indicator’s other terminal to a good ground.
- Insulate and secure all connections, reconnect the battery and test left, right and hazard functions (if fitted).
Basic wiring skills are needed: crimping or soldering and reading a wiring diagram. If you’re not comfortable working on your bike’s electrics, have a qualified technician install the kit.
Complete your LED turn signal upgrade
- Triumph Universal .45 Caliber LED Mini Markers/Turn Signal (Rear red turn signal/red running light) PN MBI-45CAL-RR, tiny 1/2″ rear LED signals
- .45 Caliber LED Mini Markers/Turn Signal (Front amber turn signal/white running light) PN MBI-45CAL-AW, the matching front pair
- Triumph Turn Signal Adaptor Wires PN MBI-0021082, for plugging aftermarket signals into the factory harness without cutting it
- Triumph Bonneville New Rage Fender Eliminator PN MBI-570992, a clean rear end for compact LED signals
Chasing another electrical fault? See our Electronic Fuel Injection EFI Diagnostics guide.
Rewires the turn indicator light to prevent feedback.
Key Benefits of Triumph Turn Signal Diode Kit:
- Allows the use of LED turn signal bulbs without causing hyper-flashing or all four turn signals flashing simultaneously.
- The diodes act as a one-way valve preventing current from flowing back through the opposite turn signal circuit when one side is activated. This isolates the left and right turn signal circuits eliminating the cross-talk that causes all bulbs to flash.
- Maintains proper operation of the dashboard turn signal indicator light.
- Enables upgrading to brighter and more visible LED turn signals for improved safety, while ensuring correct operation of the turn signal system.
- LED bulbs have a much longer lifespan (up to 50,000 hours) compared to incandescent bulbs, reducing maintenance and replacement costs over time.
Additional Items to Consider:
- .45 Calibler LED Mini Markers/Turn Signal (Front amber turn signal/white running light) PN MBI-45CAL-AW
- Triumph Universal .45 Calibler LED Mini Markers/Turn Signal (Rear red turn signal/red running light) PN MBI-45CAL-RR
- Triumph Turn Signal Adaptor Wires PN MBE-0021082
- Electronic Fuel Injection EFI Diagnostics
- Triumph Bonneville New Rage Fender Eliminator (1) PN MBI-570992
Please note: Due the nature of the product, we unfortunately do not accept returns on bearings, service tools or electrical components. Please be confident about your purchase before ordering. If you have questions, please contact us.
The product images shown are for illustrative purposes only and may not be an exact representation of the product received. Manufacturers occasionally make minor cosmetic changes to items, such as color, finish, label, or design. These changes do not impact the item’s function or compatibility. Please contact us if you have specific concerns regarding appearance.
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Frequently Asked Questions
What does a Triumph turn signal diode kit do?
It isolates the left and right turn signal circuits where they meet at a single dash indicator light. With LED turn signals fitted, this stops current from feeding back through the indicator bulb and lighting the other side, so only the side you select flashes.
Why do all four of my LED turn signals flash at the same time?
On Triumphs with one shared incandescent dash indicator, the indicator bulb connects the left and right circuits. LED turn signals need so little current that the power passing through that bulb lights the opposite side too. The diode kit blocks that path.
Will this diode kit fix hyper-flashing?
No. Hyper-flash, where the signals blink too fast, comes from a flasher relay that expects the higher current of filament bulbs. Fix it with an LED-compatible electronic flasher relay or load resistors. The diode kit fixes the problem of all four signals flashing at once.
Do I need this kit if I only change the rear turn signals to LED?
Often, yes. Back-feed through the dash indicator can still light the LEDs on the opposite side even when the front signals are still filament bulbs. If you see the wrong-side LED flashing or glowing, the diode kit will fix it.
Does my Triumph need a turn signal diode kit?
You need one if your bike has one shared incandescent turn signal indicator light on the dash and you’re fitting LED turn signals. Bikes with separate left and right indicator arrows, or that came with LED signals from the factory, usually already have isolated circuits and don’t need it.
Can I just remove the dash indicator bulb instead?
Removing the bulb does stop the cross-talk, but you lose your turn signal warning light, so it’s easy to ride with a signal left on. The diode kit fixes the problem and keeps the indicator working.
Can I replace the dash indicator bulb with an LED instead?
An LED indicator bulb only lights with current flowing in one direction. Because the dash indicator is fed from the left side on one signal and the right side on the other, a single LED bulb will usually light for one direction only. Wiring it through the diode kit, with its other side grounded, lets it work in both directions.
Is the diode kit hard to install?
It takes basic wiring skills. You connect the left and right turn signal feeds to the dash indicator through the diodes, then ground the indicator’s other terminal. Use your service manual’s wiring diagram to identify the wires, and test both directions and the hazard lights (if fitted) before reassembly.
Does the diode kit work with any LED turn signals?
Yes. The kit works on the indicator side of the circuit, so it works with any brand of LED turn signal, including the British Iron .45 Caliber LED Mini Markers.
Can I return the diode kit if it isn’t right for my bike?
No. We don’t accept returns on electrical components. Please confirm your bike has a single incandescent dash indicator light before ordering, or contact us with your model and year and we’ll help.
