low fuel light

[motowarren]

When I relaced my stock gauges I also replaced my idiot lights w/led lights 

http://www.ebay.com/itm/390561305533?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

everything works pretty good except my low fuel light stays on. I think I need to put a resistor in there but I don't have a clue what resistor. Can anybody help me?

 

[luhbo]

You can't use a LED as fuel light, not without the help of some advanced electronics. The fuel sensor requires a standard glow bulb. I know a guy who shot his sensor by playing around with resistors. It's an expensive part

I think we had a similar thread some years ago.

 

Hubert

[sp838]

Nice gauge, I got the same one! How are you liking it?

 

Kiwi_Roy actually explained to me how to use an LED instead of the stock bulb. He said to wire the original bulb in line with the LED. He can explain it much better than I can...

 

Paging Dr. Roy!

[Kiwi_Roy]

Just take one of the original lamps and wire it in parallel to the LED, tuck it in behind somewhere.

A lamp is much better than a resistor because it starts out cold at a low value, this gives the fuel level sensor full 12 Volts so it heats up quickly but the current drops back to about 100 mA.

The LED draw is insignificant compared to the incandescent.

 

I have mine wired this way, it works great.

 

What you really have to be careful of with the fuel sensor is not to mix it up with the electric petcock, on earlier bikes the plugs were interchangeable, later bikes have them keyed.

It's ok to put 12 Volts on the sensor if it's covered with fuel but it will burn out in seconds if uncovered.

 

How does the sensor work.

It's a thermistor with a negative temperature coefficient

When covered (kept cool) it just draws a few mA, not enough to light the lamp (incandescent)

Once uncovered the small current causes it to warm a little, this causes the resistance to drop so the current goes up which causes it to heat up a little more and so on getting faster and faster until the resistance drops to quite a low value. the only limiting factor is the bulb.

If you don't have the bulb in series (wrong plug) it will soon reach red heat before it melts.

It can't cause the fuel to ignite because it's in a metal can with just a tiny slot that acts like a flame arrestor.

 

Here you can see the old lamp covered in white heat shrink

 

The lamp should last forever because it gets a very easy life, no sudden turn on and never to full voltage.

[motowarren]

Thanks for the help guys

[motowarren]

Nice gauge, I got the same one! How are you liking it?

 

Kiwi_Roy actually explained to me how to use an LED instead of the stock bulb. He said to wire the original bulb in line with the LED. He can explain it much better than I can...

 

Paging Dr. Roy!

I like the speednut gauges a lot. It's nice to look at the speedo and know it's right instead of wondering whether the speedo is off or whether the tach is off today

[motowarren]

Just take one of the original lamps and wire it in parallel to the LED, tuck it in behind somewhere.

A lamp is much better than a resistor because it starts out cold at a low value, this gives the fuel level sensor full 12 Volts so it heats up quickly but the current drops back to about 100 mA.

The LED draw is insignificant compared to the incandescent.

 

I have mine wired this way, it works great.

 

What you really have to be careful of with the fuel sensor is not to mix it up with the electric petcock, on earlier bikes the plugs were interchangeable, later bikes have them keyed.

It's ok to put 12 Volts on the sensor if it's covered with fuel but it will burn out in seconds if uncovered.

 

How does the sensor work.

It's a thermistor with a negative temperature coefficient

When covered (kept cool) it just draws a few mA, not enough to light the lamp (incandescent)

Once uncovered the small current causes it to warm a little, this causes the resistance to drop so the current goes up which causes it to heat up a little more and so on getting faster and faster until the resistance drops to quite a low value. the only limiting factor is the bulb.

If you don't have the bulb in series (wrong plug) it will soon reach red heat before it melts.

It can't cause the fuel to ignite because it's in a metal can with just a tiny slot that acts like a flame arrestor.

 

Here you can see the old lamp covered in white heat shrink

 

The lamp should last forever because it gets a very easy life, no sudden turn on and never to full voltage.

Thanks Roy, Electrics is not my strong suit and I thought at first it should be wired in series but after I studied it a while I think I understand. Anyway I'll wire it in parallel.