Wiring for Fuel Gauge in Dashboard

[muwaha]

Hi All,

I was just wondering what wire(s) coming from the Fuel Pump Assembly goes to the Gas Gauge in the Cluster Panel?
The Gas Gauge basically just shows whatever it wants, I tried to manually move it to after I made sure the tank was filled, but that doesn't seem to work.

The issue was already occurring when I inherited the truck 3/4 mark meant it was filled, so I was able to judge it then.
Now Full is considered the 1/2 mark on the gauge.
I want to see if it's an actual wiring issue, or maybe the fuel level in the tank just happened to go out too quickly.
I ordered an after market Gas Gauge to see if that could help me isolate, I've searched Facebook, The Tech Forum on here, Google, and my Chilton Repair Manual, and I'm hoping I'm just blind as a bat because I cannot find these wires.

 

[franklin2]

Wire going from the sending unit to the gauge is a yellow white. It may have a orange as a ground.

If you can find this yellow/white at the fuel tank connector, what you can do is unplug the connector that the sending unit, get a scrap piece of wire and attach one end to a good ground. Turn the key to run but do not start the engine. While someone is watching the gauge, take your grounded wire and touch the terminal on the sending unit plug that has the yellow/white wire in it. The gauge should swing full scale empty or full (I forget which). Then take your grounding wire off the yellow/white, the gauge should then swing full scale the opposite way. If it passes this test, the wire and the dash gauge are good, the sending unit is faulty.

Something else you can do; I heard people talk about this, but always poo-pooed it. But my Bronco has a trip odometer on it. When my gas gauge when south, I started using the trip odometer. I figured I was getting around 20 mpg, and that I could go 300 miles on a tank of fuel. So each time I went to the gas station, I would fill up, and then set the odometer to zero. When it gets close to 300 miles, I start looking for a gas refill. Just fill it back up and then re-zero the trip odometer. It works very well and is a lot more accurate than the gauge. I fixed my gauge later on, but I now prefer to use the trip odometer for fueling.

You can start conservative, and fill it up and then run it 250 miles. Then you can see how much fuel to takes to fill it up, and figure out how large your tank is. I would always leave about 3 gallons in the tank. You can judge by each fill-up and odometer reset how you are doing on fuel versus how much is left in the tank. It's very simple once you get used to it.

 

[muwaha]

@franklin2 I've been doing the odometer triped. I can get up to 300 miles on a Full Tank before needing a refill.. I would love to see how much that is MPG but I can't find any information on how big my tank is.
It's a 91 Ranger XLT Supercab (if I didn't mention that earlier).

I will try the wire trick tomorrow, thank you for the insight!

 

[RonD]

1991 Extended cab will have a 20gal tank, actually rated as 19.5gal
Regular cabs had the 17gal, 16.5gal tank

1991 Fuel sender in the tank and gauge use these OHMs
16 ohms EMPTY
160 ohms FULL

The sender in the tank is a variable resistor, like a light dimmer or volume control, but instead of a knob it has a metal arm with a Float at the end, lol, float goes up and down with fuel level, with a range of 16 to 160 ohms
The sender has 2 wires, its connected to body/frame ground with one wire, and another wire(yellow one) runs to the gauge on the dash
So the Yellow wire is the GROUND wire for the gauge, if ground is 25 ohms it shows almost EMPTY, if its 100 ohms it shows 1/2 tank, if 160 ohms it shows FULL

Yellow wire direct to ground would be 0 ohms so gauge would show below empty
Disconnected Yellow wire would be very very high ohms, lol, so gauge would show over full

If ground wire or yellow wire was bad/disconnected gauge would show full all the time


On the back of the dash cluster in the upper right is the anti-slosh module
Google: Ford Ranger Anti-slosh module

These could cause issues with fuel gauges

 

[franklin2]

@franklin2 I've been doing the odometer triped. I can get up to 300 miles on a Full Tank before needing a refill.. I would love to see how much that is MPG but I can't find any information on how big my tank is.
It's a 91 Ranger XLT Supercab (if I didn't mention that earlier).

I will try the wire trick tomorrow, thank you for the insight!

Very simple to figure your MPG. You always fill up around 300 miles give or take. All you need to do is see how many gallons you are putting in. If you get a receipt at the pump it will have that.

So say you fill up at 298 miles. The pump says you just put in 15 gallons. 298 divided by 15 equals 19.86 miles per gallon. You do not need to know how much capacity the tank has.

Get in the truck, reset the trip odo to zero, and you can check your mileage again. I find it's the most accurate when I stop at the same station and use the same pump. It seems to cut off at a more consistent full level.