tail light out, but brake light works

[Variablevalve]

Hi guys,

I have a problem with the tail light on my 87 VFR700. I was wondering if you guys might have some insight because it stumps my very limited knowledge of how bikes work.

It's a fairly old bike, the taillight/brake lights are two light bulbs with two filaments in each bulb. When i depress either brake, one of the two filaments light up (the brake light). But when I'm not depressing anything there is no light.

I assume the other filament should be lit up all the time (as the running tail light). I only recently got this bike so I don't know much about it, but by looking at the very confusing wiring diagram it looks like the wires are all there. There's three wires.

Any help? Be kind if this is a ridiculously simple question with an even simpler answer...

Thanks

[Pittenger5]

Replace the bulb?

[Variablevalve]

The bulbs both look fine, I'll definitely try replacing them but I can't believe that they both would have broken at the same time and in a way that both only work for the brakes. Plus they both would have had to brake in an an unusual way -- so as that I can't see the brake (ie. the filaments)

[GixerJockey]

Dual element bulb. one filement is shot.

[Variablevalve]

Can the filament be shot without it actually braking? That would explain a lot...

[oVTo]

Bad flux capacitor?

["Dangerous" Dan K]

Bad flux capacitor?

I be the just needs to change the fluid, maybe bleed it out. Get the blinker fluid while you're at it. Or just replace the bulb.

[oVTo]

The bulbs both look fine, I'll definitely try replacing them but I can't believe that they both would have broken at the same time and in a way that both only work for the brakes. Plus they both would have had to brake in an an unusual way -- so as that I can't see the brake (ie. the filaments)

Buy two new bulbs and replace them to see what happens. They're cheap and if it's not the bulbs you'll have spares.

It's possible the bulbs didn't fail at the same time. One might have died years ago but was never replaced because the other still worked the bad one wasn't replaced. Now they're both dead.

If they both died at the same time then you may have a wiring problem - either an over-voltage event fried them or you have an open circuit somewhere. Over-voltage is less likely because the odds are pretty good the at least one of the filaments would be visibly open.

An open circuit is going to be at a fuse, relay, connector, or a broken wire.

Check your fuses to make sure none are blown. If one is bad, you can try replacing it to see if that solves the problem. Warning - replacing it can be slightly risky because something caused the fuse to fail, and that something hasn't been fixed. The fuse may blow again, or worse, the fuse could survive and some wiring could fry. 99% of the time the fuse will die again before any damage occurs (a fuse's only purpose is to commit suicide before any real damage is done). But I try to avoid replacing fuses if I haven't figured out what cooked it first.

Look for corrosion in the bulb socket and the connectors to the socket, then follow the wires as much as possible looking at all connectors for corrosion and make sure all the connections are still secure. On a bike that age, loose or corroded connections are good candidates for that type of problem. Look for kinks, breaks, or melted sections of wire.

I'm guessing that the VFR has a relay that shuts off the lights while it's starting. That kills both headlight and tailight, but they may be on different poles, with just the tailight part of the relay dead. Relays are easy to test, but I won't get into that here.

Once you get past the bulbs, fuses, relays, and visible wire or connector problems, it's time to get a cheapo multimeter and start looking for those missing volts. That's not difficult but I won't go into that now either.

Good luck!

[Fantastipotamus]

On my KLR650, I was having the same problem. Turns out there are two wires going into the tail lights, one for braking, and one for regular driving brake lights. so yeah, as oVTo said, you could take a look at the connections, especially if it appears the bulbs are working.

[DuncanMoto]

Depending where you live you can come visit me. I have some toold and test lights.