S2R brake light won't come on

So, I got the bike back from a service recently and a few days later a cyclist stops me to say that my tail light is "flashy". I wasn't sure what he meant (took it as a compliment at the time) but when I got back home I realised it's flashing all the time.

Just for the record, this is an integrated taillight by MotoDynamic which I've had for almost a year now and it's been working without any issues. Anyway, I pop the seat off and after a while I notice that when i move the wiring loom the flashing happens but before I could trace it down, the fuse blows.

I got a new fuse, put it in, wrapped all the connectors with insulation tape and fired the bike up. Everything works but the brake light never comes on. I've tried both front & rear levers but nothing seems to happen. The tail light is on and is a bit dim so the brake light isn't always on. Turn signals work as expected.

I figure maybe along with the fuse I blew something on the taillight so I get my OEM tailight to check and it's still the same. I doubt both front and back switches went bad at the same time so what could be the cause of this? Anything else I should be looking into?

[Saint aka ML]

Check earth cable. It is a LED set so earth is very important and corroded one will get it to do that.

On a funny note.

Switch ignition to off, press front brake and hold pressed, press rear brake lever and hold pressed.
Check if dash and rear light suddenly gets power. If it does replace that light unit as it has no suppressor and feeds 12V back to loom

[chris yeatman]

sounds like a wiring fault on the light unit.

I think the earth is ok since the tail light comes up when normally wired. Also, when I swap the brake light line with the rear light line I get the brake light always on so it seems like the electronics work on the integrated tail light. I doubt it's a wiring fault because it was definitely working at some point after I got the bike back but stopped working all of a sudden after the fuse blew up.

The only thing left for me to do is test with another brake microswitch although I'm not sure I feel comfortable dismantling both brakes so I might just take in into the shop to have a look.

[slob]

Tail/brake light and indicators share an earth (black), which as you say must be ok since indicators (white/green & pink/black) and tail (yellow) both work, my money's on a break in the brake light wire (grey/red)*.
It's possible a switch was knocked during servicing but unlikely both. It's also possible something in the light itself has failed but suspicious that you've found exposed wires under the seat, so that's the most likely place to start.

* those are the main loom colours, no idea what the colours come with the aftermarket light unit.

Finally managed to get some time with the bike and I got to the bottom of this. After having dismantled the entire light harness and made sure it's ok, just before giving up I decided to check all the fuses again and it turns out another fuse has was blown which was marked as "LOADS". Tried swapping it out with the lights fuse since they're both 15A and lo and behold the the brake light came to life. I'm not sure what else is using that fuse besides the brake light but everything else seems to work fine. Oh well...

TL;DR the brake light is not on the lights fuse, it's on the load fuse! Lesson learned

Hi fim

if it was having a flashing fit before it blew the fuse you can pretty much guarantee it has some LED's overheating/burning

they flash when resistance gets too high then come back on when cooled a little.

Most of those are PRC made and total crap quality inside even though the outer parts look fine.

Just my 2p worth.

Regards
Rick

[Mr Gazza]

LEDs are very voltage sensitive. Without wanting to sound too alarmist, I just wonder if you have had an early warning of a regulator failure?

I think it would be well worth your while to have a quick check just to be sure.
All you need to do is put a voltmeter (multimeter) across the battery terminals.

Engine off should read between 12 and 13 volts. Ignition on, it might drop a bit, but no worries.
With the engine running it should read about 14 volts. If it rises a lot above that when you increase the revs you have problems. 18 volts is definite over charge.

By all means get back on here for advice if you read high voltages, but if you do find that, it will need immediate rectification (See what I did there? ). Or you will soon have a boiled battery and possibly a fire!!

The only cure will be a new Reg/Rec... Be lucky.

[Dukedesmo]

I've got an LED taillight, no replaceable bulbs just a PCB with LEDs soldered to it.

A couple of years ago another biker told me it was flashing - turns out a link inside the light to the PCB had broken off where it was soldered to the board and it was flashing as it flicked against the solder.

I re-soldered and it's been fine but I had to split the light unit apart and then glue it back together to do so.

The vibrations probably did for it which, ironically is one reason I went for LEDs as standard bulbs tend to blow with the vibes...

Thanks for the helpful feedback guys. I don't have a multimeter so I'll get one tomorrow and quickly test the voltage readings. I'll report back with my findings!