Gen II brake light problem

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southbayninja

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Did some small electrical work this weekend and appear to have screwed up my brake light. I'm not sure exactly when the light stopped working, but here's the sequence of events:

- Installed dash cams hooked up to a relay which came on with the rear running light (via wire tap into the running light). I know for sure the brake lights worked at some point after this installation. However, the dash cams weren't happy with the power required for the starter motor and would not always record as they were supposed to.
- I tested a 10-second delay relay (simply swapped out the relays, no actual work on the bike). This was supposed to give me enough time to start the engine before drawing power for the dash cams. However, the delay relay would cut during a ride then come back on again. The manufacturer tells me this is because the tap from the running light isn't strong enough to keep the relay coil energized.
- Switched back to the regular (un-timed) relay, and instead wired into the headlight circuit so power would only be drawn to the dash cams after engine start. I did this by soldering a single wire to the headlight socket which runs to the relay activation coil. This worked well, until I discovered I don't have a rear brake light.

Symptoms:
- Running light comes on with key switch and stays on.
- Neither the front or rear brake lever/pedal causes the brake light to come on. Front headlights both work fine. It's possible the brake light is on all the time, and I simply cannot tell the difference because there is no change in the brightness of the rear light.

Here's what I've checked so far:
- Fuses are all good. Visual inspection, plus the running light is on the same fuse as the brake light so there must be a good connection if the running light comes on.
- The bulb is good: checked with a 9v battery, both filaments working.
- Retracted the rear brake light switch (next to the brake pedal) all the way, so the brake light comes on as late as possible.
- Tested the front brake switch. There is an audible click when pulling the lever, and I also removed the switch and shorted the connection- no difference in behavior.
- No codes in diagnostic memory (though I don't think any brake behavior is monitored by the main meter assembly).

Suspects:
- The delay relay that I tested caused a larger than normal drain through the running light and introduced a gremlin somewhere.
- Soldering to the headlight socket heated the stock cable (and whatever is on the other end of it) beyond its tolerance, and I've screwed up something inside the meter assembly where the cable I soldered to runs to.

Any ideas anyone?
 
I can see that only one filament on th bulb is lit up, not sure which one though. Also not sure if both filaments come on when the brake pedal is pressed, or if the bulb switches to the brighter filament whilst the brakes are applied and then reverts to the less bright one. Knowing that might help me trace the problem.

Anyone?
 
I would start with the cheapest option and try a new globe just to make sure it isn't that. The worse case scenario that way is you have a spare bulb.
 
Maybe the tap at the brake light severed the OEM wire to the point it is making no contact with the tap itself? Since this was the main point of access, I would remove that tap, cut the OEM wire, solder it back together with an added pigtail to connect any aftermarket item to and use shrink tube to seal it back up. Before you heat seal the shrink tube, test the brake light function. If all is well, seal it and use the added pigtail to attach accessories to.
 
Let's break this down to the basics.

The rear tail light has 3 wires to operate.

12V to iluminate tail light (blue/red)
12V switched brake (yellow)
Ground - black

So I would check that when you actuate a brake switch, you get 12V on the yellow wire.

Good luck,
 
Turns out a number of things had transpired against me, and I'm still not certain I understand precisely what happened, but:

The bulb was good - replaced and tested resistance to confirm
The switches were both good - checked voltage and resistance, also shorted both switches to simulate a press of each brake
The lamp holder is good - checked voltage and resistance to confirm. However in doing so I accidentally shorted a connection with my multi meter lead and the rear lamp went out permanently.

I checked the fuses and the headlight fuse was blown. Swapped in the spare fuse and bingo, rear brake light is back. What is strange is I rode home that day and the headlights were working fine. I had checked the fuses when the issue first arose and they were all good, so I'm not sure why shorting the rear lamp would cause the headlight fuse to blow, or why the rear brake light did not work when the headlight fuse was still intact. I did notice that the fuse box layout for the FZ1-N is different to the FZ1-S and the service manual is not super clear at pointing that out. Subtle difference but important to know.
 
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