Brake Light Wiring for aftermarket light

[Party Cat]

Hate to be that guy who jumps a forum and asks a question right away but I'm about to start to post myK100 build and am stuck on one wiring issue.  So...here's my question and I'll begin by mentioning I am terrible at wiring lol:

I am trying to install an aftermarket single bulb non LED tail light.  The light has 3 wires (red, black, and green) and I'm taking the following to be true for the K100 wires: Brown is ground the grey with a black stripe is the tail light and the grey with a yellow stripe is the brake light.  I have connected the brown ground from the bike to the black ground on the light.  I can get the tail light to work by connecting the grey/black white from the bike to the red wine of the light.  I can get the brake light to go on by connecting the grey/yellow wire from the bike to the red and green wires while the grey/black is still connected to red.  If I just connect the grey/yellow to the green I get no change or just connect grey/yellow to the red.

Now here's the dilemma:
I can't get the light to signal brake (brighter bulb signal) by using either brake lever.  I'm not sure if I'm missing something in my wiring technique or if I have removed a wire somewhere along the way that would connect the brake pedal/lever signals from reaching the yellow/grey wire. 

I have stripped down my '91 K100LT including some of the wiring so that's a possibility.  I basically removed the ABS computer and any other plug ins from the front loom that were used for antenna, speakers, instrument cluster, etc.  I have not unclipped the brake lever signal wires (should be pairs of yellow wires that clip into green/black wires and a light bluish on one and something else on the other...

To rule this issue out I was thinking to run the brake lever signal wires directly back to the light somehow but as I'm crap at wiring :dunno, any tips on this idea or other ideas on this would be rad.  Thanks in advance foe the help and PARTY ON!  :riding:

[Party Cat]

I'm gonna try to eliminate one possibility and gauge my dumb dumb level by testing the signal on the oem 2 bulb tail light tomorrow am.

[Motorhobo]

Is the OEM taillight you're connecting to a dual-intensity light? I think the OEM taillights use a 1157 dual filament. Single-intensity bulbs will give you single intensity regardless of how you wire them but I'm sure someone will correct me if I'm wrong about that.

[Party Cat]

I'm pretty sure the oem light has single intensity bulbs.  I'm reasoning that's why there are two of them (one for tail and a secondary for brake).  The after market light is dual intensity.  I'll check with the poem to see if I'm getting brake signal as I was afraid that was the issue.  Now that I'm reflecting on it I can't remember anything lol so yeah fresh start tomorrow with higher brain function hopefully.

[Motorhobo]

Yeah of course the flasher is single intensity...I've been working on making my single intensity sidecar tail lights function as dual intensity lately hence the brain fart. If your aftermarket light is single intensity incandescent, then that's probably going to be a problem. If you use an LED you can make a simple circuit with a resistor and diode that will make the LED function as dual intensity. I got it to work but I didn't have the right resistors on hand...I have a resistor assortment on order -- will post to the forum if I can get it to work properly.

[Party Cat]

So here's an update.

I have tried using a separate bulb for the brake lights (similar to the oem 2 bulb system) and with the blub grounded plus connected to the grey/yellow signal wire, it works sometimes...and only with the kill switch set to full on position.  It'll work twice with foot and hang brake then stop working.  If I disconnect it and re wire it and turn the kill on/off I can get it to work a couple times more...seems like it's got a faulty wire somewhere in the line but not sure where to look so any ideas just shout it out!  Thanks for the help dudes and dudettes!

[Party Cat]

Spoke with the shop I got the light from and they mentioned there may be a problem related to the bulb wattage even as another possibility.  The bulb I was experimenting with was a front indicator bulb.  I will try tonight with the correct tail light bulb and see if that makes a difference.

[Party Cat]

Odd finale...

I tested the oem bulbs and the tail light bulb 5W would not work with the brake signal.  The oem brake bulb 21W did work.  I started thinking about reverse retrofitting the poem bulb but tried the dual filament setup once more.  For some reason it works now...don't know if I just got too dumb last night or if taking apart the aftermarket and reassembling it had to do with it.  It is a 2 post dual filament so possibly one post was not making good contact previously...in any case not it works properly and I took it out for a first ride!

[ts888]

Sounds like you got it working, but I have some aftermarket LED lights mounted on the luggage, with green/yellow/brown wires, and brown was not ground...  I tested to determine the actual function of each wire on the LED light, then wired accordingly to the brick wires.