How To

Run/Turn Lights On One Bulb

Many motorcycles use dual filament bulbs in their front turn signals that operate as dimmer steady-on running lights when the brighter signals aren’t in use. I could only find single filament turn signals in a hurry for my Honda Shadow ACE when the aftermarket light bar shorted out, so I lost both my driving and running lights and just had the single headlight left. I just stumbled across a way to not only regain the original functionality but also extend it to the rear turn signals.

A single headlight is all that’s legally required for the front of a motorcycle, but there are disadvantages. Amber running lights on either side clearly proclaim “I am a motorcycle” rather than “I am a car with a burnt out headlight.” Additionally, a single point of light makes it difficult for others to determine how close I am and how quickly I’m approaching. I’ve definitely been cut off more frequently after removing the faulty light bar, whose running and driving lights made it much easier for others to judge my distance. I’d wanted to replace my temporary turn signals with Lowbrow Customs’ amber dual filament bullet lights to match the red ones I already put on the back of my bike, but they’ve been out of stock for a while, and when I asked when they’re getting more they said they didn’t know.

I was watching various motorcycle videos on YouTube the other day, and the title of a suggested video caught my eye: “How to have a turn signal and running light in 1.” This is quite relevant to my interests, so I watched it.

He faced a similar issue, where his fancy new LED mirror/turn signals could only be turn or running lights, not both. He demonstrated that by connecting the power wires for the turn signals and running lights together, the single light would serve both functions. The problem was that this fed running light power back through the turn signal circuit to light up the rear signals as running lights as well. Amber running lights are illegal on the rear – they have to be red. So he added diodes to the circuit to only allow power to flow in one direction. The fronts remained combination turn/running lights, and the rears were turn signals only.

But wait – I’ve already changed my rear turn signals from amber to red. I tapped power off the license plate light for the dim filaments to make them additional red running lights, and wired the normal turn signal wires into the bright filaments. On a recent New England Riders group ride, my group’s sweep rider politely informed me that these rear turn signals weren’t particularly visible to her, and suggested that I might want to see to that. Over the winter I planned to run new running light wires from the front to the back of the bike so that they, too, would shut off when the turn signals were on, just like the front. But I realized that if I simply connected the run and turn wires together without the diodes shown in the video, my rear turn signals would become running lights, using the bright rather than dim filament for added visibility. Since they’re already red, they’d be legal tail lights, unlike the bike in the video. So rather than adding wiring, I removed the custom running light wiring I’d already added to turn off the dim filaments in the back. The bright filaments are even brighter running lights, and located far enough away from the run/brake light to not obscure it when I’m braking. When I signal for turns they flash on/off rather than bright/dim, solving the visibility issue. I’m not using the dim filament at all now, but that’s OK. The dual filament lights were the same price as the single filament ones, so it’s not like I wasted money.

I spent more time undoing my wiring with the rear lights than I did modifying my front lights to serve double duty. That was maybe a five minute job for both sides since I already knew how that wiring worked. After doing one side, I, too, had the issue shown in the video where the turn signal indicator was constantly on, but after doing both sides this was no longer the case, at least on my bike.

Since this modification affects the rear turn signals too, no additional wiring is necessary. If your rear signals are red, you’re done. If not, you may be able to swap from amber to red lenses, or use red tint on your amber lenses. I understand that a contrasting color like amber is more clear as a turn signal than red. But my tail light isn’t huge, and I’m willing to make the color trade-off to gain two additional tail lights that double as turn signals.

Lowbrow Customs amber bullet light

This also means I no longer have to wait for Lowbrow Customs’ dual filament amber bullet lights to come off of indefinite backorder. Instead I bought a pair of single filament units to replace my temporary turn signals up front. (I got the last two they had in stock, which is why I jumped on them immediately.) They’ll match my bike better, and are larger and more visible than the dinky little lights I have now (the NER ride leader also mentioned he had trouble seeing my front signals – hopefully this will fix that too). They’ll also serve as both running lights and turn signals, now that I’ve figured out how to tweak the factory wiring slightly to enable that functionality.

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