LED bulb problem - CB77

Seadog · Post by **Seadog** » Tue Dec 08, 2015 10:05 am

I've swapped out every incandescent bulb on my CB77 to LEDs and now have a problem that I hope those more electrical knowledge than I can help with.

My problem is with the high beam indicator. With all LED bulbs - headlight included - the indicator is lit fully with the high beam on and dimly when the low beam is on. If I change the indicator bulb back to incandescent, the same holds true, but if I change just the headlight bulb back to incandescent, all works as it should.

Could there be some sort of back feed problem when using the LED headlight bulb?

I've checked all ground connections and even added jumper wires from the headlight frame and the indicator bulb socket to a frame grounding strap to be sure. That does not help.

None of the LED instrument bulbs are polarized. Would a polarized high beam indicator bulb help?

I'm lost here.

jensey · Post by **jensey** » Tue Dec 08, 2015 11:54 am

What kind of LED headlight do you have ?

Seadog · Post by **Seadog** » Tue Dec 08, 2015 12:51 pm

It's a Cree. My knowledge of LED headlights is sadly lacking. I'm missing something.

revlover · Post by **revlover** » Tue Dec 08, 2015 2:37 pm

I think you're on the right track with current being feedback through the LED headlight bulb. If you think about it, a standard incandescent headlight is actually two bulbs in one with separate filaments. The same is probably not true with the LED bulb. Adding a silicon diode between the bulb socket and the high beam lead may correct your problem, as the diode only permits current flow in one direction. If you do that and your high beam fails to light, simply reverse the polarity of the diode. In order to choose a suitable diode, we must however know the current draw of your LED headlight bulb and select a diode with a geater current rating. Hope this helps.

48lesco · Post by **48lesco** » Tue Dec 08, 2015 2:41 pm

I know less than you about LED's but that doesn't stop me from rendering an opinion. The indicator gets 12V off of the high beam wire so there must be a small voltage there when you apply 12V to the low beam side. No diode is perfect, there's probably some voltage "leaking" from the low to high beam circuits in the bulb itself. Could be on purpose to always keep some current flowing in the high beam. Don't know, just fun to speculate.

Seadog · Post by **Seadog** » Tue Dec 08, 2015 3:43 pm

Thanks for the reply, revlover. The specs say 8 watts.

Voltage: 12v AC/DC
Color: white
Led chip: 5w*3pcs cree led in four sides+4pcs cree led in top side=80w(16pcs chip)
Power consumption: 8w
Brightness: 800LM
Liftspan: 65,000 hours
Diameter: 18mm
Low power consumption.
Easy installation, just plug & play.
Light weight, long lasting.
Direct replace old filament bulbs (no wiring)

revlover wrote:I think you're on the right track with current being feedback through the LED headlight bulb. If you think about it, a standard incandescent headlight is actually two bulbs in one with separate filaments. The same is probably not true with the LED bulb. Adding a silicon diode between the bulb socket and the high beam lead may correct your problem, as the diode only permits current flow in one direction. If you do that and your high beam fails to light, simply reverse the polarity of the diode. In order to choose a suitable diode, we must however know the current draw of your LED headlight bulb and select a diode with a geater current rating. Hope this helps.

Seadog · Post by **Seadog** » Tue Dec 08, 2015 3:46 pm

You don't sound like you know less than me! 😃 Seriously though, I think that there is voltage leaking back too. The question is how to stop it. Someone must have figured this out before.

48lesco wrote:I know less than you about LED's but that doesn't stop me from rendering an opinion. The indicator gets 12V off of the high beam wire so there must be a small voltage there when you apply 12V to the low beam side. No diode is perfect, there's probably some voltage "leaking" from the low to high beam circuits in the bulb itself. Could be on purpose to always keep some current flowing in the high beam. Don't know, just fun to speculate.