I did a little search and learned a little but still stuck as how to proceed.

I am replacing the rear tail light unit on my 97 XLH. I have the old on off and noticed it has three wires a black, wire a blue wire and a red/yellow wire. The new unit only has two wires and red and black. How might this work for me. I mean is there a way to make it work.

Ric

 

Ok, I have tested with temporally connections. I have a carry over problem but first question is the brake the bright or the dim filament? I know dumb question. I'd think it would be the bright one but need confirmation.

2nd thing the reason this job got started was that both filaments were burning all the time and burning out the bulbs. When I took off the fender I could see the black ground wire was worn through and not connected so I assumed that was the problem with the brake light stuck on. aberrantly that was not it as it is still happening with the new light and wiring. I guess it is maybe at one of the lever switches. Any tips on how to check that?

 

I was able to disconnect the rear break easy enough and to no avail. It is going to require a little more work on the front, in that the wires are strung through the bars. I will get to that tomorrow.

 

Seems doubtful. The black wire is ground. The other two are power, one for the brake light and the other for the taillight. The blue one is the taillight. Older bikes have two lines, but they are the taillight and brakelight, neither are black. They are grouned locally. Newer bikes have the ground wire so the TSM can detect faults, i.e. burned out bulbs or shorts, and report it to the driver as a safety feature.

If you look in the socket likely you'll see one post at the bottom, but if you look in the old one you'll see two and two at the bottom of the bulb. If the new one came with a bulb you'll likely see there's one filament. I would assume that works by burning brighter and dimmer depending upon the power supplied over the one wire. You might be able to pull the socket out of the old one and place it in the new one.

 

LilBudywizer, What seems doubtful? You don't think the two wire will work? what is older or newer. my bike is a 97 and on the diagram in the manual there are 3 wires as I described.

 

Older is two wire plus a local ground. Those two are green and red with the local ground being black. Two wires, one red, one black, would indicate one power (red) and one ground (black) by convention. That power would indicate one filament. Black, blue and red/yellow is newer bikes. Red and black? I don't know, maybe really old bikes like 80's or 70's. I've heard of people having the same problem you do, but what those assemblies go to I have no idea. What's doubtful is that you'll get it to work. To use it you'll have to choose between a taillight or a brake light. You can, most likely, just go back to the light you were using. It was shorted, fix the short and the light works fine.

 

Well, I should have mentioned that I had to replace the tail light it self because one of the mounting studs broke off. That's how I happened to have the new unit laying around waiting to go on. So you don't think that the two wire unit was designed to be a tail light break light? That seems unlikely to me.

Thanks
Ric

 

No, I think it's designed to operate off a single power line. The voltage/current on that single line determining whether it burns bright or dim on a single filament. If so then that isn't how your bike works. Your bike has two seperate power lines for two seperate filaments.

My guess is that it's a standard housing they just stick whatever socket is appropriate in and ship out. Contact whoever you got it from and they'll likely swap what you have for the right one. If the old socket fits in the new housing then use that. With mine to change the bulb you have to remove the socket. Give it like a quarter turn and it pulls out. Perhaps over tens years things changed. With my '94 the lens cover comes off and you remove the bulb from the socket. Hehe, I sat in a parking lot in the middle of night bitching that there was no way to get to the bulb before I figured out the socket just comes out though. Then I bitched about a bulb I could only buy from harley.

PS: Then I bitched about a corroded circuitboard I had to order and wait for it to arrive.