Reroute the wire from the dash to the LED. You may have to use a resistor to drop the voltage.

 

ya, but the stock dash and tach are no longer - I'm using aftermarket speedo.. otherwise that would be the way i would do it.

It apears the circuit board does the triggering from the res. value from the sending unit.

 

This works in my mind & seems like the easiest way. It is speculation on my part.

Hide the low fuel light under the tank & connect the led to it. Both of them should light when you get low on fuel.

 

quote:Originally posted by Churchkey

This works in my mind & seems like the easiest way. It is speculation on my part.

Hide the low fuel light under the tank & connect the led to it. Both of them should light when you get low on fuel.






true, but since the stock dash is no longer, i need to pull it from the sending unit directly.

 

...but do you still have the light from the stock dash?

 

Slothy - I'm an electronics tech, maybe I can help. From which page in the Service Manual r u getting this information? I can't find it. If you can identify which wire from Speedometer harness connector goes to the LED, you can use it to light another LED.

 

no, being it was part of the dash. and even then i woulda had to break it apart and use the circuit board to it.

basically i need way to trigger a relay or someting along that line based off of resitance values

 

quote:Originally posted by MrWilson

Slothy - I'm an electronics tech, maybe I can help. From which page in the Service Manual r u getting this information? I can't find it. If you can identify which wire from Speedometer harness connector goes to the LED, you can use it to light another LED.


section
7-52

fuel sending resistance @ while empty @68 degs

900-2050 ohms

 

First I think you need to know what is actually reading the signal from the sending unit and controlling the action of lighting the low fuel LED. If the 'intelligence' for this is in the ECU then you should just need to figure out the mechanism that is used for lighting the LED in the speedo and copy or emulate it. If the 'intelligence' is in the speedo then you will need to provide both the reading and setting functions. I would hope that the intelligence would be in the ECU and the speedo would just house the mechanism for turning on the light. You should be able to verify this by looking for a signal(or wire)from the low fuel sending unit at the ECU in the manual or schematics. In this case it should be something similar to what MrWilson said and you should be able to find the correct feed wires to the speedo and setup the conditions that the ECU wants and you should be able to light a low fuel LED I would think. Of course there is the possibility that the ECU is sending digital data to the speedo which is interpreting and then taking action on it in which case you are SOL(unless you want to build a digital decoder box) but this seems like overkill for a bike so I suspect more of a regular 'analog' approach. Just my 2 cents worth.

 

i know the wire(s) and the conditions as mentioned before.

just was hoping someone in here knew how to use resitance values to trigger something.

 

quote:Originally posted by slothy


quote:Originally posted by MrWilson

Slothy - I'm an electronics tech, maybe I can help. From which page in the Service Manual r u getting this information? I can't find it. If you can identify which wire from Speedometer harness connector goes to the LED, you can use it to light another LED.


section
7-52

fuel sending resistance @ while empty @68 degs

900-2050 ohms


The way that is worded it sounds like you would have to build a circuit that would query the fuel sending sensor by sending a known voltage/current through it and then measuring the changes in order to determine the R value, and then when the R value falls within the correct range, send current to the LED.

I would bet that the ECU does this for you and that you just need to find the correct lead from the ECU, and then, depending on what the output of that lead is either connect it directly to your LED or a resistor and an LED.

 

ya i check diagram, the output from the sending unit goes directly to the tach and then to speedo. (so maybe the tach is the one doign the conversion) - oh well i was just hoping it would be a few diodes/resistors/caps wire em up and wala.. Guess not hehe

 

Slothy, I checked over the diagrams in the manual. It looks to me as though the Fuel LED is connected through one of the wires (G/R , green/red?) in the blue connector on the wiring harness from the TACH. See page 7-44 , Signaling System Circuit Diagram, part #40, lower right hand corner. It looks like 12 volts will be supplied at all times by wire BR (green connector) and that the ECU provides a circuit ground through wire G/R when the fuel hits reserve level.

Test this with a volt meter as shown on page 7-53, upper right hand corner. Connect to G/R (Fuel)instead of Gy (Engine Trouble), as shown. When you first turn the key to the "on" position, the meter should go to 12V-15Vdc for a second or two. If it does, Hooray!

Now you can go to Radio Shack and spend $2 on an LED such as Red LED w/ Holder Catalog #: 276-084. You must get one that is built for 12 volts. It should have a resistor already inside of the holder. Connect the + wire to the green connector Br and the - wire to the blue connector G/R. Try it with the ignition key test. If it works, your all set. Let me know.

 

Use a 100K - 110K ohm and a 10K ohm resistor in series. Attach the cathode between the resistors. Attach either resistor to the 12 volt source(trigger voltage) and the other end of the resistor combo and anode of the LED to ground. If this is too dim, switch the resistor values to 10K and 1K. This is a basic voltage divider. The first combo provides 100 micro amps and the second provides 1 milliamp. To go brighter, you need only adjust the total resistance down while maintaining a 12:1 ratio of resistors. Formula: Voltage divided by Resistance(OHMs) = Current(Amps). .001 = 1 milliamp, .0001 = 1000 micro amps. The LED you purchase should show MAX current draw on the package. Alter the formula to determine Minimum total resistance, then use the 12:1 ratio to find closer values. Use 1/8 Watt resistors with a +/- of 10%.
Example: Max current = .0025 AMPs, 12 divided by .0025 = 4800 Ohms or 4.8K ohms. Your values are now 4.8K ohm and 480 ohm. Basic OHM's Law.

 

BSWFT : I don't understand your reason for having 12:1 ratio between the two resistors or why you would need two resistors at all. For a fixed total series resistance, say 2000 ohms, the current through the LED will be the same whether you use a singe 2k ohm resistor or ten 20 ohm resistors. A single resistor is all you need.

 

quote:Originally posted by MrWilson

BSWFT : I don't understand your reason for having 12:1 ratio between the two resistors or why you would need two resistors at all. For a fixed total series resistance, say 2000 ohms, the current through the LED will be the same whether you use a singe 2k ohm resistor or ten 20 ohm resistors. A single resistor is all you need.


MrWilson, you are correct with the total current but what is issue is the working Voltage of the LED purchased.
Most LED's operate at .7 volts dc. If you apply 12 volts to them they burn out. The 12:1 ratio in the voltage divider not only provides the proper voltage but also limits current with total resistance. IF, a 12 volt LED is used, you will only need 1 resistor to limit the current using OHM's law to determine the size of the resistor.
For example: From A to B to C, 12 volts is applied at A and ground to C. A-B resistance is 1000 and B-C resistance is 200. The Voltage measured from A to B will be 10 volts, the voltage from B-C will be 2 volts, while voltage measured from A-C will be 12 which is total applied voltage and the sum of A-B + B-C. These are mathmatical values but actual values will be within a volt or so.
(The "-" is not minus signs).

 

thanks guys - ill let ya know how it goes

 

got it ! the tach sends the dash a +12 signal when there is gas, and when it kicks to low level it turns the signal to 0V. So what i did was take a 12v relay and wire it up to trigger output when it see 0V on the input

 

oops here is diagram



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