Taillight but no Brakelight...

[Guest]

I searched the forum and found one other post regarding this, but my situation is slightly different...

I am reassembling my '77 GS 750 and purchased a new brake/taillight to replace the broken original. The new light has red, black and yellow wires. The original has white, black w/ stripe and brown wires. My assumption is that red and white, black and black w/ stripe, and yellow and brown go together. Any idea if this is correct? Once hooked up, I'm getting the taillight but no brakelight. I tried numerous configurations with the wires and got bright and dim taillight, but never a brakelight. does this seem like a ground issue somewhere?

Thanks!

[Steve]

Sorry, but there is one big problem here:

... My assumption is ...

With three wires coming out of the light, it would be a good guess that it is, indeed, a dual-filament light setup.
You can play around with guessing what wire does what (my guess is that the black wire is the ground wire)
or you can simply open up the light and see what goes where.

You might also find that some Bozo has assembled your light with a single-filament bulb.
Or you might find that your brand, spanking-new bulb has a bad filament.

Regardless, you will be able to verify for yourself which wire is for the ground,
then connect that to a battery and see what the other two wires do.

When you find what they do, the brown wire on the bike is the tail light, the white wire is the brake, the black/white is ground.


NEVER ASSUME.

.

[Toasty]

The ground wire isn't hooked up correctly, find the combo of two wires that gives you a dim light when the headlight is on and then run a ground wire to the frame (or to the stock ground wire).

[GS750cafe]

It's definitely a dual filament bulb. It gets brighter or dimmer with various configurations of wires, just not when the brake is actuated.

Toasty, I'll try your approach.

Thanks

[Steve]

It's definitely a dual filament bulb. It gets brighter or dimmer with various configurations of wires, just not when the brake is actuated.

OK, that tells me that the light is fine, look for a problem on the bike.

Do your turn signals work? Does your horn work? No, these are not silly questions, they are all powered by the same fuse.

If the light works with one brake (front or rear), but not the other, you have a bad switch.
If the light does not work with either brake, but your horn and signals work, you have a broken wire, possibly in the headlight bucket.

.

[GS750cafe]

OK, signals and horn work, but I've got the headlight removed and am building a gauge mount - signal, oil warning and neutral indicators. I wasn't going to have a highbeam indicator or gear position indicator. Could it be that without all these hooked up, I'm not getting a brakelight?
Neither front nor rear brakes light it up...