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Brake light seems to be always on

R

Robokopp23

Just got it firing!
Joined
Oct 5, 2024
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Location
Cologne, North Rhine-Westphalia,Germany
So I bought a used Mandello with 3300km on the clock. When I did the test ride everything seemed to be ok and the previous ownder did the 1st inspection at 1250km so I tought there is nothing to worry about.
But now the brake light seems to be always on. Or at least there is no change when I activate the front or rear brake. Tested in multiple situations to see if I am just dumb, but wether the engine is running or not, there is no change in the rear light intensity. Even made my wife drive behind me to see if there was any change :D

Checked for the obvious things like loose cables or a fuse but I couldn't spot anything. There are also no error messages on the dash when I turn on the bike. The switch on the rear brake also seems ok, meaning that when I push the rear brake I at least hear a little clicking noise. While studying the manual I learned that there is no actual switch for the front brake, but that pulling the brake leads to a pressure changee that is recognised by the ABS-Sensor, which then communicates with the 11MP-ECU.
The only thing I noticed was that the battery was low, but when I charged it there was also no difference. Did this occur to someone else and was there an easy to fix or do I have to go to dealer so they can check? I am able to do basic maintenence but as beautiful as the bike is, its a driving computer and I am worried of doing even more damage by looking for mistakes.
Like I said everything beside that is running just fine. Any advice or help appreciated.

If there is no easy fix then I will have to go through a dealer, but its just annoying not to be able to ride with just a few warm days left in the year. I also called some dealers near me and they only have time in about 1-2 weeks.
 
Is there a way to power the brake light directly from the battery?
Should be, but it requires that the lights are powered by 12Vdc and not a weird plc system signal.
 
Good question. I had a short look at the light but the Signal for the brake comes from an ECU and the rear unit is full LED as far as I could see. So no dedicated wire for the brake light it seems to me.

But I have to say I didn't disassemble the rear light yet. If its possible I would like to avoid that for now.
 
My Roamer was like this (bought with 3000 miles on it) the tail light wires were on the brake light and brake light wires on the tail terminal, check the wiring.
 
I'm not sure you can disassemble the rear light, looks like a completely sealed unit, on the plug under the seat there are 3 wires going into it, one is an earth and the other two are for the tail light and brake light. Its not on the CAN bus so unplug it and use a meter to see if your getting volts on the respective pins.
 
Thanks for all the replies so far.
Yeah its a sealed unit. I will give it a try tomorrow and check the wiring. Unfortunately don't have time today. I already disassembled part of the rear yesterday and saw the plug but I gave up after that and put everything back together. But it's good to know that there is at least a dedicated wire for the brake light even if it is coming from an ECU
:D

Regarding the brake fluid level is that a real option? I mean the Front Brake signal apparently is being actived by a change of pressure in the brake line but just the level of brake fluid applying enough pressure?

My plan for now is trying to reach out to a different dealer tomorrow and if he has an earlier time slot available then I will leave the bike as is. If the only available time slots are in 2 weeks then I will give it another try and check the wiring.

I will let you guys know whats the outcome and thank you again for the replies so far :)
 
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A pressure type brake light switch is a normally open switch. With an increase in pressure, the circuit is closed. If your brakes are not dragging, then it isn't from brake line pressure
 
So a quick update from my side. I managed to get hold of smaller shop near me. Not an official Guzzi Dealer but at least he was able to connect to the bike via OBD.
At least it seems there is nothing wrong with actual brake switches/actuators as he saw all the inputs from the brakes on the diagnostic device.
So I guess the fault must be somewhere between the taillight and the ECU that needs to output the signal to activate the Brake light. Which hopefully is not as expensive to fix as an actual problem somewhere in the brake circuit. It also seems that the Brake light is always off. So maybe just a faulty LED or taillight unit?
If thats the case then I guess I need to replace the whole rear unit as its all LED, but I guess thats how it is with the modern bikes.

I just managed to go there on my lunch brake and was happy that the shop took the time right then and there to at least have a look and short diagnosis. Left the bike there now and hopefully they have the time this week to run further trouble shooting. If its something expensive that needs to be replaced I will try to sort this out via warranty as the bike is still under two years old.

But hopefully its something that can be fixed easily and I will be able to ride the bike at least for a few days this year.
Thanks again to everybody so far for your inputs :)
 
If your aren’t more than a few hours ride from a Moto Guzzi shop I would take it back to them for Warranty repair,before I started taking things apart :wasntme:.

I don’t know why “They” think it’s best to run everything through a computer , rather than have a simple switch and wires connected to a light.
( Yes - I was a Luddite in a past life -
Look that man is using a Lever !
Off with his Head :blush: )
 
Its not even about the distance of the Guzzi Shop. But the ones I called only have timeslots in the beginning of November and before that they won't even look at it :(. I know I'm impatient here, but having the bike just standing around for a month doing nothing just bothers me too much :D I would at least like to know whats the error here. I told the shop, they should just run the diagnosis and if its something bigger then I will go down the warranty road. So fingers crossed its something that can be fixed easily.

I work in automotive so I know how things are done sometimes. If they are able to safe components, in that case a dedicated front brake switch when they instead can use the already existing ABS Sensor for that, then thats a business case.

Definetly not against computers and I knew what I was getting when buying a V100 but yeah its kind of frustrating. On the other side I get a lot fancy functions with all those computers :D
 
Huh, nearly a month, well that is certainly annoying.
Can you trace the wire to the sensor on the ABS unit to check if it’s functioning as it should ?
( never mind about tracing anything once it gets into wiring loom… :cry: )
 
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On the OBD you could at least see that front brake lever was sending the right signals. So the ECU is at least receiving the right signals from the brakes. Now I would assume its a matter of getting the output signal to the lamp. But like I said hopefully that is easier to fix than an actual problem within the brake circuit.

So the shop is now tracing wires and see where the signal is stuck. Fingers crossed its something inexpensive or a lose wire somewhere. I hope/guess worst case would be a defect taillight that can be replaced.
 
Hey Guys. Just to put some closure on this topic because I also don't like when you are searching for info and then finding open ended threads :D
So it was a faulty brakelight and because the whole unit is sealed and LED the shop had to replace the whole unit. Will try how the guarentee works since I did the work in an unofficial Guzzi shop. Lets see.
But spending the money now instead of having to wait two more weeks for diagnosis and replacement from an official Shop was too much for me. At least like this I get to have at least some rides this year. Lets hope from now on its smooth sailing and thanks again for all the suggestions :)
 
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