Topic: CB750 K4 LED Tail Light Help

[ZettabyteGA]

Hello all, so I just converted my bike to all LED's. I replaced the blinker flasher with an LED compatible one and installed diodes to fix the 4-way flashing problem. I have run into one problem I can't seem to figure out on my own. I replaced the rear 1157 tail light with an LED and it simply will not turn, and I can't figure out why for the life of me. The same 1157 LED bulb will work in the front turn signals but not the rear, I have also confirmed that the socket and wiring still works by putting the old incandescent light back into the rear light socket. Any ideas on how I can get this LED light working? I will link the LED light in question bellow.

https://www.superbrightleds.com/moreinfo/tail-brake-turn/1157-led-bulb-dual-function-27-smd-led-tower-bay15d-bulb/2625/9034/

[Bodi]

I've used this type of LED lamp and it just worked.
Is the socket OK? Maybe the contact plate is stuck in a bit or won't move, the old lamp could be a bit deeper than the LED one so the contact isn't made?
I don't think there's any way to miswire the socket because the outer tube is grounded to the frame. But if it is possible and somehow polarity is reversed with ground on a contact and +12 on the tube... an LED won't work, they need the correct polarity power.

[bryanj]

The rear indicators are single filament single contact unlike the fronts

[spotty]

Have you checked with a battery or charger that the led bulb actually works
Just a thought, I"ve chased a few wiring problems only to find out that the component was shagged not the wiring

[BenelliSEI]

I’ve had a similar issue. Look closely at the dimensional photo on the vendor’s website. I’ve attached it here. The upper lock pin appears higher than a stock 1157 bulb? It is! And will never work in your socket. Measure the pin heights from the base, same problem?

I did get one to work, by filing down the contact points at the bottom. This allowed the pins to drop deeper in the socket....... good luck!

[ZettabyteGA]

I've used this type of LED lamp and it just worked.
Is the socket OK? Maybe the contact plate is stuck in a bit or won't move, the old lamp could be a bit deeper than the LED one so the contact isn't made?
I don't think there's any way to miswire the socket because the outer tube is grounded to the frame. But if it is possible and somehow polarity is reversed with ground on a contact and +12 on the tube... an LED won't work, they need the correct polarity power.

I tested it with a multi meter and everything's wired correctly in the socket, so that inst the problem unfortunately. The bulb is making good contact with the pads, and to make sure I manually pushed out the contact pads and pushed the bulb onto the little pads and still no light sadly.

[ZettabyteGA]

Have you checked with a battery or charger that the led bulb actually works
Just a thought, I"ve chased a few wiring problems only to find out that the component was shagged not the wiring

Good advice, but I have confirmed the bulb actually works. The front signals use the same bulb and I have switched them out a few times and they always work in the front turn signals.

[ZettabyteGA]

I’ve had a similar issue. Look closely at the dimensional photo on the vendor’s website. I’ve attached it here. The upper lock pin appears higher than a stock 1157 bulb? It is! And will never work in your socket. Measure the pin heights from the base, same problem?

I did get one to work, by filing down the contact points at the bottom. This allowed the pins to drop deeper in the socket....... good luck!

I had to do the same thing with the two on the front, unfortunately I don't think that's my problem with this rear lamp. I am able to get the light to twist and lock into place it just wont illuminate unfortunately. It is just baffling me why this wont work, the incandescent works perfectly but nothing from the LED. I really just don't know why.

[ZettabyteGA]

I’ve had a similar issue. Look closely at the dimensional photo on the vendor’s website. I’ve attached it here. The upper lock pin appears higher than a stock 1157 bulb? It is! And will never work in your socket. Measure the pin heights from the base, same problem?

I did get one to work, by filing down the contact points at the bottom. This allowed the pins to drop deeper in the socket....... good luck!

When you say you filled down the contact points you mean the actual power transfer pins at the bottom? Or the littler side pins?

[BenelliSEI]

I actually filed the bottom contacts a little bit. That allowed the lamp base to drop a little further into the socket. Then, the pins lined up deep enough so I could just rotate the bulb into place.

If the led bulb works on the bench, and the stock bulb works in the socket, then there is only a few options: The LED bulb is either not making contact with the two signal pins in the bottom of the socket (poor alignment or not deep enough) OR the bulb is not grounding in the socket........

[ZettabyteGA]

I actually filed the bottom contacts a little bit. That allowed the lamp base to drop a little further into the socket. Then, the pins lined up deep enough so I could just rotate the bulb into place.

If the led bulb works on the bench, and the stock bulb works in the socket, then there is only a few options: The LED bulb is either not making contact with the two signal pins in the bottom of the socket (poor alignment or not deep enough) OR the bulb is not grounding in the socket........

Thanks for that info, it is greatly appreciated. I'll try grinding the bottoms a bit and see what happens.

[BenelliSEI]

Good luck, be patient and make sure the contact is there for both signal wires and the ground.

[ZettabyteGA]

Good luck, be patient and make sure the contact is there for both signal wires and the ground.

Okay, I'm hoping you can help me out here. So I thought the bulb might not be getting grounded properly due to corrosion, so I took out the yellow/green and brown wire (which are the live and neutral I believe) and hooked them up directly to the new LED bulb, still no light. I kept those wires connected and then touched a different grounded wire to the metal shell area and the light turned on instantly! Unfortunately the light is only one brightness level, applying the brakes does not make it get brighter. So I tested the old incandescent bulb with that same setup and the same thing happened, it light up but did not get any brighter when the brakes were applied. So the original ground wire is somehow the reason the second filament lights up when the brakes are applied and the light gets brighter. Any idea at all how I can fix this issue and get it working with an LED?

[bryanj]

NOPE
Yellow/green is brake light power
Brown is running light power
Green is ground

[ZettabyteGA]

NOPE
Yellow/green is brake light power
Brown is running light power
Green is ground

Is my bike wired up wrong then? Because the brake light wont turn on unless the original ground is connected, I can't use a different ground. Or am I just doing something dumb.

[bryanj]

The ground is through the casing of the bulb to the bulb holder then usualy a braided wire to the big lamp base and the ground green connects to that via a spade terminal hidden when light bolted to bracket.