gingerbreadmaniac


not sure if the previous went through proper so ill try this one




On my 85 f150 The gas gauge didnt work (oh its on propane) So i started snooping at it. i found the wire from the propane tank in the back of the box ran down to where the old gas tanks were and spliced into the old wires. The wire from the harness underneth to the propane tank was corroded so i ran a new wire to the old gas tank wire. The gauge then worked but was innacurate (it read 1/2 full when full) It started to not work,and as i played with the front and rear tank switch on the heater control it seemed it was shorting out or wasnt grounding properly. so i pulled the dash apart unhooked the switch and taped into a wire i found had power, i grounded that wire and the gauge went right to the end of the gauge on full. I started playing and i hooked up my 12 volt light tester between this wire and ground and the gauge worked perfectly. When i turned the ignition on the light would stay on full as the gauge went to its proper position and it would start blinking when the needed was where it should be and would start blinking untill i turned the ignition off. The way it is now is i took a dash light and mickey mouse wired it in, to see if it was accurate through a tank of fuel and it is so i would like to do something properly now.

Could i use a resistor or something?
What amount of resistance will i need if that is the case?
Am i going into uncharted territory that is going to light my trucks wiring harness on fire?
Any ideas would help me out a lot
thanks
josh

 

I looked at my diagram for 84-86 trucks, and it seems the wire you want, is a yellow/white wire. This wire comes from the guage, but does not go to the selector switch. This fuel guage wire goes directly to a "motorized selector valve". I would guess this valve might be located along the frame somewhere. You need to find it, and get the yellow/white wire that runs to it, and hook it up to your tank. It seems the selector switch tells the motor valve which tank to select, and the valve itself switches the guage from front to rear.

 

gingerbreadmaniac

If i remember correctly the wire i choose from the selector switch was yellow and white. I taped into this wire and ran to ground and the gauge went right to full, i then added a light bulb and the gauge works perfectly right through the tank of fuel. i dont know why but its that way now and it works perfect. i would like to wire it properly so could i use a resistor or something????

thanks

josh

 

If your truck is wired like a 1984 or earlier, yellow/white still goes to the gauge, and does go to the switch, and then a dark-blue/yellow goes to the front tank, and a yellow/light-blue goes to the rear tank. The guage should be hooked up directly to the sending unit. If you have to have the rig you put on, to make it work, then the fuel guage is not compatible with the sending unit in the tank you have. Consider yourself lucky you got it to work at all if this is the case. There would be a way to figure out and eliminate the bulb, and put a resistor in, but I don't know if you have the means to do it. While the circuit is on, you would have to measure the voltage ACROSS the bulb to see how much voltage you are dropping by using the bulb. Then you would have to measure how much current the circuit is using. You would have to put a meter in series with the bulb to measure the amps (probably a fraction of an amp) the bulb is using. With these two values, you could use the formula E=IxR where E would be the voltage drop measured, I would be the amps measured, and R would be the value of the resistor you are looking for. Say you measured 3 volts across the bulb, and .5 amp through the bulb, then a resistor that would be equivalent would be 3/.5=6 ohms. The size of the resistor in watts would have to be in this case, P=IxE so .5 amp x 3 volts =1.5 watt resistor.

 

gingerbreadmaniac


yes the wire that i ran from the propane tank was dark blue\yellow and it ran to the switch. i than spliced into a yellow white wire directly off the switch harness and grounded that wire, when i did that the gauge read full than between that splice and ground i wired in a bulb (my lighttester) and it works perfectly.
What wire did i tap into?
and where did it go to?
and why does it work properly?

i am going to draw a simple picture and maybe you could explain how i would go about measuring this , as i do have a meter that is fairly accurate. for that picture i will email it to anyone who wants and maybe because i do not know how to add it to this message. if you would like this simple drawing email me at

joshherman2@home.com

thank you
josh