Electrical 1156/7506/etc. -Dual use for single filament bulb!?
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1156/7506/etc. -Dual use for single filament bulb!?
I notice that the running (parking) light and brake light are the same one-filament 1156 bulb in the tops of my 2009 R55 Clubman's tail light assembly.
I figure that the CanBus sends a lower voltage (probably about 6 volts) for running light performance, and kicks it up to 12 volts when you hit the brakes.
When I measured the voltage with the running lights on and the bulb out, I got only about 1 volt, which isn't enough to light the bulb as bright as it is in the circuit in running light mode.
Maybe there needs to be a load on the socket from the bulb for the CanBus to send the right voltage to the socket, or maybe it's current limited.
The wiring diagrams in the Bentley manual are not helpful in figuring this out.
Anybody know the scoop? And why didn't they just use a 1157 dual filament bulb like most combo running/parking light applications do??
BTW, am thinking of swapping in a pair of 3497 bulbs, (Honda's P/N 34903-SF1-A01 is apparently better quality than other 3497s) for brighter brake light performance.
They are 27W instead of 21W and put out significantly more lumens due to their higher wattage and better efficiency as well.
Anyone else do this yet?
I figure that the CanBus sends a lower voltage (probably about 6 volts) for running light performance, and kicks it up to 12 volts when you hit the brakes.
When I measured the voltage with the running lights on and the bulb out, I got only about 1 volt, which isn't enough to light the bulb as bright as it is in the circuit in running light mode.
Maybe there needs to be a load on the socket from the bulb for the CanBus to send the right voltage to the socket, or maybe it's current limited.
The wiring diagrams in the Bentley manual are not helpful in figuring this out.
Anybody know the scoop? And why didn't they just use a 1157 dual filament bulb like most combo running/parking light applications do??
BTW, am thinking of swapping in a pair of 3497 bulbs, (Honda's P/N 34903-SF1-A01 is apparently better quality than other 3497s) for brighter brake light performance.
They are 27W instead of 21W and put out significantly more lumens due to their higher wattage and better efficiency as well.
Anyone else do this yet?
I ran into this several years ago when trying to connect a trailer light adapter onto the MINI I had at the time (an 08 MCS). I’m pretty good with auto electrics I think and was completely stumped why I couldn’t get the wiring to work. Using a multimeter i was getting crazy readings depending on what mode the lights were in.
This type of lighting is pretty common nowadays I think especially now that there are more stock LED systems in cars. It’s called Pulse Width Modulation. In short, it changes the voltage sent to bulbs to control the brightness.......so single filament bulbs are used instead of dual filament as a result. One of the main reasons manufacturers use it is for cost savings.....less wiring involved. It’s cheaper to have electronic control of the lights rather than run extra wiring to illuminate another filament. It also makes things like tail/marker lights that dim slowly as they turn off (like when you press the lock button on the remote) possible.
As i recall, the issue i ran into on my 08 was that depending on the key position (on, accessory, etc) the lights behaved differently. Some that were brake lights in one mode wouldn’t be in another mode and vice versa. I finally ended up tapping the marker lights for tails and found the lead that went up to the stop light on the boot hatch for brakes.
doesnt help with your bulb choice......but that’s the situation on the single filament bulbs as I understand it.
This type of lighting is pretty common nowadays I think especially now that there are more stock LED systems in cars. It’s called Pulse Width Modulation. In short, it changes the voltage sent to bulbs to control the brightness.......so single filament bulbs are used instead of dual filament as a result. One of the main reasons manufacturers use it is for cost savings.....less wiring involved. It’s cheaper to have electronic control of the lights rather than run extra wiring to illuminate another filament. It also makes things like tail/marker lights that dim slowly as they turn off (like when you press the lock button on the remote) possible.
As i recall, the issue i ran into on my 08 was that depending on the key position (on, accessory, etc) the lights behaved differently. Some that were brake lights in one mode wouldn’t be in another mode and vice versa. I finally ended up tapping the marker lights for tails and found the lead that went up to the stop light on the boot hatch for brakes.
doesnt help with your bulb choice......but that’s the situation on the single filament bulbs as I understand it.
Last edited by Fastlane; Aug 22, 2018 at 05:02 PM.
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