Tail Light Operation question [kz650b2]

on a 1978 kz650 b2, is the running light really supposed to extinguish when the brake is applied, or are the low- and high-wattage filaments supposed to light simultaneously? I don't see anything in the wiring diagram that would cause the low-wattage light to go out when the brake is applied, but this is occurring on my bike. I am just discovering this and am not sure of the cause; I am having trouble getting an LED bulb to function correctly in that socket, but it works pretty good in a front turn signal socket, where the lights are simultaneous. I don't know if that difference is by design, or if I did something bad wiring in a replacement switch earlier this year, or if maybe I have a bad connection?

Any thoughts appreciated, thanks
nathan

I think that's normal. I could be wrong, but I don't know of any dual filament bulbs in which both filaments light up at the same time. Maybe it would generate too much heat or draw too much load. Ed

I suspect a wiring problem or the sockey for the bulb has gone bad.The brake and running light are seperate circuits.

Color codes:

RED, the tail light or running light circuit.
BLUE (sometimes with a red stripe), the brake light circuit.
BLACK with YELLOW stripe, the ground circuit.

650ed wrote:

I think that's normal. I could be wrong, but I don't know of any dual filament bulbs in which both filaments light up at the same time. Maybe it would generate too much heat or draw too much load. Ed

The front turn signals operate both filaments simultaneously.

MFolks wrote:

I suspect a wiring problem or the sockey for the bulb has gone bad.The brake and running light are seperate circuits.

That they are. The brake light failure indicator is wired parallel to the brake light circuit also, and as such, when disconnected it has no effect on the tail light or brake light function. That is, not until the LED bulb is inserted. This issue is driving me NUTS. I had no problem with the turn signals, and I would really like to use it in the tail because it is much brighter than a filament bulb when it is in a compatible circuit. Guess I'll do some continuity checking and terminal cleaning.

Sounds like the socket is old and/or the ground portion is weak. You can verify this with a voltmeter. If you have roughly the same voltage to ground, with the light out, when the brakes are applied, the ground/ground connection is weak. If you lose the low wattage voltage source then you have a different problem.

You may not notice it as a ground problem because the high watt side does light. What you may not notice is that it isn't as bright as it should be with a good ground connection. The high resistance ground is dropping more voltage when the high wattage filament turns on making the low wattage filament appear to go out.

The ground for the front and rear lights are two different connections. Technically, the problem could be upstream of the low wattage side, but is less likely (it is fed directly from the ignition switch).

If I'm not mistaken, the turn signal lights share the same 5 pin connector in the back. If the turn signals coming on don't dim the tail light, take a closer look at the ground wire coming off the socket (the black/yellow wire) or the socket itself.

[quote]650ed wrote:

I think that's normal. I could be wrong, but I don't know of any dual filament bulbs in which both filaments light up at the same time. Maybe it would generate too much heat or draw too much load. Ed

sm0kinace wrote:
"The front turn signals operate both filaments simultaneously."

You're right, I was wrong. :blush: They say you learn something everyday, so I can relax the rest of today. I checked and like the front turn signals, both filaments of the tail/brake light are lit at the same time when your lights are on and you hit the brake. My bike is a '77 C1 but would think the '78 B2 should be the same. Ed

Alright, thanks for your help guys, but here comes the part where I tell you vital information that I omitted and that was useful in solving the problem. First, can anybody tell me what model this tail light housing is from?



a PO had installed this...I think it looks great, much better than the original square housing. Problem was that the wire colors are different, he had 2 splices between the factory wiring and the socket, and most importantly the ground and brake wires were swapped. Polarity fixed, incandescent bulb works correctly, and LED bulb works great! It is definitely brighter.

I was only able to order the LEDs in pairs. I only have use for one, and seeing as it will likely outlive the bike I doubt I will need the other. PM me if you want it... 1 1157 Red LED.