Weirdness from LEDs

I had a few burned out bulbs in the instrument panel so I replaced them all with LED bulbs since the speedo and tach are a pain in the butt to get at. I did turn signals too which work fine after a quick flasher relay replacement.

All of them work fine, except two bulbs, the fuel light and the brake light. These two shine dimly constantly. I've switched bulbs around on the brake light and it does that with any LED and not just with the bulb that is in there. They get brighter when they are supposed to be on. I put a normal bulb in the brake light slot and it doesnt glow dimly.

Has anyone seen this before? The brake light I don't care about seeing, but the low fuel light is hard to see in daylight with a normal bulb.

I'd first throw a multimeter on the line. Obviously there's power being sent thru it, but it'd be great to know how much and why. If all else fails, and you're only worried about the light glowing when not in use, you could always stick a resister in the circuit. Not optimal tho... :whistle:

Also, check both the low fuel sensor and the brake light switch. Make sure that both of them are good by testing voltage across them while on/off. Good luck!

I’m not the electric expert here. I know that bikes with brake light out warning relays don’t like LED’s. The relay senses the resistance of the filament in the bulbs and knows the brake light is working. I think it’s also reading the combined resistance of both dash indicator bulb and brake light bulb. By changing to LED’s you alter the resistance and the relay is thinking the brake light bulb is partially out thus the dim glow. If that make sense. You still have resistance but not enough.

Knowing that fuel level devices work the same way as reading resistance you might have the same problem by changing resistance in the circuit by swapping in an LED.

I don't work on gauges much, but if the fuel light is the type using a solid-state sensor, you will need a ballast resistor to get the circuit to function correctly. The original light bulb is meant to act as a short, or a very low resistance, which heats up the sensor when the fuel level drops below it. When the sensor heats up, the resistance of the sensor drops and the light comes on.

You would need an appropriate resistor in parallel with the LED. This will make the LED turn off, and will cause the sensor to heat up properly when it's no longer under fuel. If you still have the original light bulb, you can measure the resistance of the bulb and get a resistor of the same ohm reading. The wattage rating of the resistor will depend on what the resistance (ohms) was, so if you post it, we can figure out what wattage resistor you would need.

For the brake light, you no longer need a brake light warning for a filament being out. But you may still want the brake light on the dash to come on to tell you the brake lights are on. For that, one option is to replace the brake flasher unit with a relay. The details are in this thread:
www.kzrider.com/forum/4-electrical/61047...83-kz440-ltd?start=0

Oh I think I get it now. The bulbs were being used as resistors in addition to creating light, and by switching to LEDs I have increased the resistance changing the circuit. I was afraid I had some sort of weird shorts that were pulling those circuits up a little rather than it being intentional design.

I'm trying to avoid tampering with the original wiring much and keeping what I do easily reversible, so i might just put the original bulbs back in those two sockets. I need to look at the wiring diagrams and think about if its worth the effort or not.

I think I am going to buy a spare idiot light cover and dremel out the blue plastic for the high beam light and replace the bulb for the high beam dummy light with a little blue .28 inch voltmeter so I can monitor voltage easily whenever by just switching on high beams.

Because it comes up so often, I had assumed you had replaced the brake lights with LED's as well. But now I realize you didn't mention doing that. That relay option was specifically for running LED brake lights, not necessarily for an LED dash indicator, though it would work for that too. But then it no longer detects the filaments of the brake lights.

Changing the brake warning flasher to a relay is really only an option if you are running LED brake lights. If you are running incandescent bulbs then you probably want a filament indicator working.

Adding LED idiot light reduces the circuits resistance. To get them working correctly measure the resistance of the original filament bulb and add in a resistor of equivalent value in parallel across the two bulb holder input wires.

Using LED's increases resistance, which reduces current. You then add a resistor in parallel which reduces the overall resistance which increases current.

Got my resistance and current back to front. Its not called electrickery for nowt.:blush: