A maze with no exit (brake light wiring)

[misterprofessionality]

Let me lay out some circumstances for those of you who may or may not have ever attempted to put an aftermarket rear brake light on your cb1100:

You have a Green/yellow wire, a Black/brown wire, and a Green wire.

The brake light has a Red wire and a Black wire.

So, the goal is to figure out which two wires attach to the Black and Red wires and which one is left unattached (the ground). Of course, we don't live in a world where wire colors make any sense or live by any form of consistency, so i thought "trial and error right?" wrong. I've now blown two fuses, i think i've tried every possible color combination in the universe, and I still can't figure out why this won't work.

The best result i've gotten and the only thing close to success: When attaching the green wire to the black and the Green/yellow wire to the Red, the brake switch activates and the light comes on. I've taken the red cover off so I can see the actual bulb filament ignite.

When I swap these wires to their opposite positions, the brake flasher switch STILL works in the exact same manner, and the same bulb filament ignites.

I have never succeeded in getting the bulb to light up when the black/brown wire is attached at any position.

The bulb, upon visual inspection, appears to be in perfect working order, both filaments.

CB1100 forum: WHAT DO I DO?

[Cormanus]

I'd start [url=http://cb1100forum.com/forum/showthread.php?tid=13353&pid=217528#pid217528]here, although I have no idea whether it will make any sense.

For what it's worth, it looks to me like the green/yellow wire should control the brake light. The black/brown light looks to control the tail light and the green is the earth.

Are you sure the aftermarket light allows both functions? I've got all sorts of theories, but Lord Popgun or max or peterbaron or one of our other wizards will solve it for you.

[misterprofessionality]

The aftermarket light does have both functions, based on the fact that the bulb has two separately actuated filaments.

I've seen all the wiring diagrams, but i can't make any heads or tales of it other than to say i think you should be correct that the green/yellow wire delivers power from the brake switch.

If the black/brown wire delivers power to the running tail light, then why can i get no operation at all whenever it's hooked up to either wire?

[pekingduck]

If you have only two wires from the new taillight, a red and a black, the red goes to the green/yellow for the brake. The taillight black goes to the brown/black for running light/taillight. The body of the taillight grounds through the metal fender.

When you hooked the red to the green/yellow, and the black to the green, and hit the brake pedal, both filaments were lit, the brake light brighter so you didn't notice the taillight filament.

The power was coming in through the green/yellow, through the brake light filament to the bulb's shared metal casing, into the taillight filament, through the black wire and into the green ground wire.

[misterprofessionality]

Thanks for the input Peking. Everything you said makes sense save for one thing.

"When you hooked the red to the green/yellow, and the black to the green, and hit the brake pedal, both filaments were lit, the brake light brighter so you didn't notice the taillight filament."

see, i have the bulb exposed for this reason, because i wanted to see which filaments are lit up. in fact, only one filament is lighting up in this case. You said i just didn't notice because the other one was brighter but i can confirm that the lower filament is not lighting up at all when i hook the Green/yellow and the Green up.

Does this change your assesment?

"the red goes to the green/yellow for the brake. The taillight black goes to the brown/black for running light/taillight."


Can you offer any explanation as to why when I hook the Green/yellow to the red wire, and the Black/brown to the Black wire, no filaments light up at all?

[Ben70_imp]

misterp, don't want to assume anything. You are grounding the body of the new light, right? it isn't being insulated from the fender somehow?

Ben

[pekingduck]

My assessment changes slightly regarding the taillight coming on. I went to verify it, and the tail light does not come on, but power is running across it. Basically when you have the black and red hooked to the green/yellow and the green, both filaments are in series. The brake light filament has 1/3rd the resistance of the running light, (so it is much brighter). The taillight filament just acts like a wire.

But on a headlight bulb, where high and low beams are closer in resistance, both filaments will light. I just verified that.

When you hook the Green/yellow to the red wire, and the Black/brown to the Black wire, no filaments will light because they are both hot wires coming in, and neither filament has a ground.

[Cormanus]

So, in this new arrangement, what do you do with the green wire on the bike end of the plug? According to the wiring diagram, it heads off to the regulator / rectifier.

[pekingduck]

So, in this new arrangement, what do you do with the green wire on the bike end of the plug? According to the wiring diagram, it heads off to the regulator / rectifier.

The green on the harness side can be disregarded - it doesn't ground the reg/rectifier, it just taps into the same common ground wire.

[Cormanus]

Thanks, pekingduck, that makes sense. Except that with the Honda OEM light, surely it completes both circuits? How is that supposed to happen with the new arrangement?