autometer fuel gauge PROBLEM!!!

[SRT_DSTRHOLC]

OK so i have a tach already, so i thought all i have to do is splice into my tach wires to hook up my fuel gauge. I did that, but when i go to turn my lights on the fuel gauge pegs to the black metal screw past fuel and it pegs REALLY fast, but then when i turn the lights off it goes back to the correct spot marking how much gas i have. I have no clue whats going on.

I have the the Igniton wire off the fuel gauge connected to the Red wire off the tach. The White wire for the lite bulb is run to the white wire on the tach. Then the ground off the blub is spliced into the wire of the fuel gauge then spliced into the ground off the tach. And then the Sending unit wire off the fuel gauge is ran all the way to the gas tank, to were the stock hook up was.

I have no idea why when i turn the lights on the gauge pegs and then when i turn it off it's fine. Do i have to run the Ground off the light blub to a seperate ground or what? All help welcomed

 

[70Duster440]

Did you install the tach? You're drawing power from it's wiring and you're sure it's correctly wired?

Disconnect the the fuel gauge. You should use a volt/ohm meter and/or a test light to verify that you have +12v on the red wire only when the key is turned on. Verify that you have a proper ground to the chassis. Verify they you have +12v on the wire for the light bulb only when the headlights are turned on.

If these are all good and you're sure you're connecting the wires to the correct terminals on the fuel gauge, then the only thing left to check is the fuel sender wire - which sounds like it is shorted to a ground somewhere.

If you connect an ohm meter between the sender wire (at the dash) and ground, you should have a reading somewhere between 9 and 75 ohms or so. If it reads 0 ohms, that wire is shorted to ground somewhere and you'll have to trace it.

 

[SRT_DSTRHOLC]

ya i installed the tach... It should be correctly wired becasue it's working perfectly fine.
do you think i have to run the light ground to a different ground?
or maybe the problem is in my pas wiring?
the gauge works perfectly when the lights are off and car running, but when i turn the lights on is when it goes crazy but the tach is fine

 

[SRT_DSTRHOLC]

i got this off autometer
"All Auto Meter fuel level gauges and most OEM fuel level gauges operate on the same principle. They operate the same way as an ohm meter and measure resistance to ground, but only within a calibrated range and direction. Power & ground is supplied to the gauge to power the meter. A signal is produced on the “S” terminal, which is then connected to the fuel tank sending unit. The fuel tank sender then receives that signal and varies resistance to ground. The sender can be thought of as nothing more than a variable resistor. This is why the sender also needs to have a 2nd wire going to a common chassis ground, otherwise the sender would not have the ability to vary resistance to ground."

it says gauge is powerd by power and ground then wire to sending unit in tank, but it says something about a 2nd wire going to a common chassis ground. does this mean i hook the gas tank sending unit to another ground on the chasis?

 

[70Duster440]

Don't ground the terminal on the sending unit to ground but the main body needs to be grounded which is usually via a metal strap clamped between the fuel sender hose fitting and the fuel line (that's to complete the ground circuit across the short rubber hose - and that's what they're talking about). If you ground the terminal on the sender, your gauge will peg.

Try running a separate ground wire - like, from your dash frame, to the ground terminal on the fuel gauge. Don't use what you think is the ground wire in your lighting circuit - unless it goes only to the light bulb. Sounds like you're running voltage through a terminal you shouldn't. Again, with the gauge disconnected, you should probe each wire to see what's actually going on when you turn the lights on.

 

[SRT_DSTRHOLC]

ok thanks

 

[SRT_DSTRHOLC]

o the other thing is since i spliced into the ground wire for the tach, the tachs grounded straight to the battery.....is that waht it might be?