so lately the soobs been acting up a little, lying about how much gas is in the tank the suddenly going HEY IM EMPTY! then yesterday it quit reading all together, so i crwled under the rear bumper and sarted tracing the wiring back, and low and behold, THE DREADED RIGHT RIGHT CORNER!!! duh nuh nuh! and found that someonelse had issues with it because you know how the rear defogger and sending unit share the same wiring harness (yep!) well it had been so corroted they just wired the defogger direct with a crimp, so I pulled out the ol' electrical tester, and found that I'm not getting any power from the Inst. panel down to the sender, I first noticed this at the first wiring harness you encounter when tracing backwards from the tank. Like I said, the dreaded rear panel harness.

 

So at this point, I'm wondering why I'm not getting any power from the instrument panel.

 

Also noticed the voltage gauge is reading obserdly low on the dash, but my sunpro gague reads around 14. This just started yesterday with the fuel gauge going out.

 

Am I not getting ENOUGH power to that area of the Inst. panel?

Very Kindly let me Tell you that if you're expecting to have Power (12V+) on the Wires that goes from the Float Sender in the Fuel Tank, to the Instrument Cluster's Fuel Gauge, You're So Wrong.

 

That wiring only carry Ground Signal... and trying to put Power (12V+) to the Float sender could be Very Dangerous! ... ... Imagine a Spark inside the Gas Tank...

 

So, if your No Reading / Low Reading fuel Gauge issue, started along the Voltage Gauge reading Low, your Subie's only electrical problem is the Alternator: It isn't Charging the Battery anymore...

 

Kind Regards.

I just changed alts a month ago, And installed a Sunpro voltage gauge, which reads around 14 volts with the car running, while the dash only shows around 8volts. This is unusual and just noticed it when the fuel gauge quit reading.

 

 

+--->O----->+-------->0--------\\\

If i understand correctly 12 volts should be supllyed to the fuel gauge, that 13 volts is passed through the gauge and down to the sending unit, the sending unit is also grounded. The gauge will measure resistence in the sending unit, created by the float and distance from the metal band that completes the circuit.

 

Are you sure there is no power going to the sending unit?

Are you saying that this is nothing more than a ground circuit, composed of a ground passing through the gauge, and down to the sending unit?

You can't expect 12v at the sending unit because there is voltage drop across the gauge. Due to that you can't test for voltage at the sending unit because your test would be meaningless. You have to pull the sending unit out and test for resistance as you move it through it's range.

 

The stock voltages gauges often read low. They simply aren't very accurate. You can't rely on that reading - you need to measure voltage to the instrument panel with a meter.

 

GD

Check fuse 13.

Bad dash power supply or possibly ground is causing the low voltmeter readings.

 

Sender wire should be 12 volts unplugged.

7 volts w/a 7 ohm resistor subbed for the sender.(full tank reading)

Oops! ... Double Post! ... My internet connection Sucks... Sorry, look the Right Post, Below.

Edited January 28, 201313 yr by Loyale 2.7 Turbo

... Are you sure there is no power going to the sending unit? ...

 

GD Did explained it Better than I:

 

You can't expect 12v at the sending unit because there is voltage drop across the gauge. Due to that you can't test for voltage at the sending unit because your test would be meaningless. You have to pull the sending unit out and test for resistance as you move it through it's range. ...

 

 

... Are you saying that this is nothing more than a ground circuit, composed of a ground passing through the gauge, and down to the sending unit?

 

No, what I tried to explain is that the Power (12V +) Imput to the Circuit of the Fuel Gauge is Directly supplied to the Fuel Gauge "Needle" Coil at the Instrument Cluster, while the Ground (12V -) for the Circuit is supplied by the Sender unit's Float, at the Fuel Tank.

 

The Position of the Sender Unit's Float, Determines the Amount of Ground on the Circuit, which makes the Needle to point Low at Low Ground = Low Float Level on the sender, or the Needle will point High at High Ground = High float Level.

 

Sometimes a Bad Alternator makes all the Gauges to Read Low...

 

Kind Regards.

Edited January 28, 201313 yr by Loyale 2.7 Turbo

So I am playing around with a similar problem. Though my sending unit was rusted solid cause the car was sitting for a while. When jump the circuit It should make the tank read full correct? I am presuming when I install the new sending unit it will still not work. If this happens what next?

So I am playing around with a similar problem. Though my sending unit was rusted solid cause the car was sitting for a while. When jump the circuit It should make the tank read full correct? I am presuming when I install the new sending unit it will still not work. If this happens what next?

If you connect the sending wire that goes to the sender to ground it should peg the gauge.

Got it by connecting all the dots...  Above I grounded the gauge and it pegged.  Installed the new gauge and was jumping up and down that I did not waste 85$