I'm looking to wire in an additional brake light on a top box. But looking at the existing wiring to the rear light unit I can only see one live wire and an earth.
Baffled as to how one wire sends 2 signals, some kind of voltage/amperage boost for the brake light ??? (or am I perhaps suffering a senior moment)
There is an earlier thread re Givi topbox light but it relates to earlier model bike.
As far as I can see, there should be about 5 wires in the harness going to the rear of the bike, including earth, number plate light, rear light and two indicators.
I'll have to get under the rear plastic cover and have another good look. The rear light is an LED unit which only seems to have one connector ????
I'll post some photos if I'm still struggling.
The diagram shows the complete wiring harness for the twin with (2) being the part that goes to the back of the bike. I'm assuming the connector that plugs into the rest of the wiring harness has 5 wires going through it.
I've just had a look at the rider's manual which shows a picture of the underneath of the seat. It's not that clear but is the harness not taped to the left-hand frame tube?
It looks as though the LED rear light option may well be CanBus controlled via a twisted pair harness. If so, you would need to navigate the complexities of how CanBus controllers work in order to be able to add the additional brake light:think:
Oh dear, that sounds rather tricky and brings back a memory of an electrical fault I caused on a 2000 model R1100 by trying to break into a wiring circuit !!!
Maybe I'll manage without the extra brake light
Many thanks
If it does have a twisted pair of wires going to the back of the bike, even I would leave it well alone - and that's from a spacecraft engineer who's supposed to understand these types of wiring systems:think:
My understanding is that the rear light uses Pulse Width Modulation (PWM) on the CanBus to switch between the tail light and the stop light - it's all at 12V but the PMW reduces the average voltage to nearer 6V for the tail light.
Another option would be a deceleration switch. Wouldn't have to tie in to your existing wiring. Could go straight to battery thru a fuse. Wouldn't activate when parked so no need for a switched power lead. It appears to be a mercury switch, and is adjusted for different sensitivity. If you or a friend are handy with wiring, this would be a good option. https://rimmerbros.com/Item--i-DRC2332
The pulse width modulation makes more sense than voltage control I will put a scope on the tail light when I get hold of another can bus bike to verify this and report back, maybe even some screen shots of the signals.
The PWM simply causes the LED's to pulse in the same way with a higher duty cycle producing a brighter light - this is because the response time of the human eye only sees the average light level. However, you should see the effect of the pulsing using a digital camera?
I think I now understand the electrical system on the F650GS twin (and later F800GS etc) which is not straightforward because of its use of a CanBus network to simplify the wiring.
In terms of the rear lights and indicators, the CanBus itself is not used to control them as such. The F650GS twin uses a conventional harness with ~5 wires going to the back of the bike. Where LED lights are fitted (brake/tail or indicators), a pulse width modulated signal is employed to control the brightness - in the case of the lights, 100% duty cycle for the brake light and ~50% duty cycle for the tail light. That signal is generated by the Central Chassis Control Unit which can also be referred to as the CanBus Controller.
The complication in fitting an additional stop light is that the CanBus Controller monitors current use in order to sense faults and therefore the current use of the additional light needs to be taken into account. It's probably not that hard to sort out but is much more complicated than a system using incandescent light bulbs!
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