Topic: Electrical Question: Brake Light Which Wires

[mauserfan]

I'm replacing the big honking tail lights from an 1982 CB900c with an Emgo Cats Eye tail light.  It has three wires, Red (brake), Black (dunno), Yellow (dunno).   I've tried multiple combos and cannot get the running tail light to work.  The Red Emgo wire to the Honda Green/Yellow stripe works the brakes, but the Brown Honda wire doesn't seem to do anything.  What am I missing?

I've got it grounded (through the mounting studs of the Emgo light fixture).

The Emgo doesn't come with a wiring diagram. Does anyone know what the proper combo is?  Do you need a photo?

[Frostyboy]

Doesn't sound like it's a SOHC that we're used to, however try running the black wire to ground. Does the brown wire have power when tail light on?. You might also want to check the bulb is okay, even if it is a new one.

[mauserfan]

Continuity yes, volts no. I am using the rear half of a wiring harness from a parts bike. The existing harness / lights work so I have either a bad rear harness or it requires a special circuit setup. I'll have to post a pic of the wiring diagram and harness.


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[kirkn]

Wait - is your question about the Emgo wiring or about the bike's?

For the Emgo - do a little disassembly.  It ain't rocket science.  One wire goes to one tit on the bulb, one wire goes to the other tit on the bulb, one wire goes to ground on the bulb socket.

Using jumper wires, you can test the bulb itself.  (-) battery terminal to the body of the bulb.  (+) terminal to first one tit, then the other.  The tit that lights the light brighter is the brake light one.  Now you know which wire does what on the Emgo.

As for the bike, you're kinda on your own there.  On the stocker, there were either two or three wires, depending on if the brake light 'body' was itself grounded to the fender.  I'm betting there were three - one for ground (green??), one for tail light power and one for brake light power.

BTW - welcome aboard!

Good luck with it, and post back what you find.

Kirk

[Xnavylfr]

If you have Tail Light power hooked to the Brake lght side of the bulb you won't be able to tell if the tailight bulb is lit due to the brightness of the brake light.

I always check power on ALL lights with a battery charger before I install on the bike and then label the wires.
Hook the negative to the mount itself for ground then just touch each other wire with + to find out what wire goes to what.
Most  aftermarket lights use black as ground, brown as tail light power and red as brake light but you never can tell.


Xnavylfr(CHUCK)

[mauserfan]

Well I finally got it.  The yellow is ground (weird).  I took it apart to find out (thanks guys).

The tail wasn't working because I had blown yet another 15Amp glass fuse without knowing it.  Tested by putting the wires strait to the battery as described (thanks guys for jogging my thought process).  So I knew at that point the fixture and bulb was good. And worked backwards from there.

Image attached.