Gas gauge buried beyond full mark

[Das Ding]

Hello,
I have researched everyone's previous gas guage issues here but have not found one like mine.
When I turn my key on the needle goes all the way to the right and stays there.
I have a new sending unit, new guage needle, and new regulator.
I have the sending unit in my lap at with it grounded to the dash and a new wire from the sending unit to the regulator.
Still the same condition.
I take off the wire from the sending unit and turn on the key and the needle goes to the right past "Full".
Could there be more than 12vdc going to the regulator?
What are your thoughts?

[mondshine]

Either your wiring or your description of your wiring is wrong.

The black wire that provides battery voltage (when the ignition is switched on) to the indicator lights at the bottom of the speedometer continues on to the vibrator. From the vibrator (which switches power on-off-on-off a couple of times per second) reduced voltage continues on to one of the gauge terminals.
The other gauge terminal is grounded through the tank sending unit, which is actually a wire wound rheostat that provides varying resistance to chassis ground based on the position of the float.

The brown wire in the sketch labeled 31 is actually the wire to the fuel sender (which is providing varying resistance to ground).

Good luck, Mondshine

[Das Ding]

Thank you Mondshine.
I will get on it.

[heimlich]

For all OEM parts you would need to turn the screw on the back of the gauge. This helps set the gauge correctly. It's very small and hard to get to but on the back of your gauge look inside the hole. There is a piece that moves left to right.
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[Das Ding]

I ended up bypassing the vibrator with the power from the ignition switch on one terminal and the wire from the sender on the other terminal of the fuel guage.
I adjusted the sender limits by bending the legs or tabs on the sender.

[heimlich]

What the vibrator does is smooths out the signal as the gas is moving around so the needle doesn't go up and down. For example when you are making a turn.
_________________
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Classic Brands. Classic Quality.
Not all parts are made the same. NOS OE/OEM parts made mainly in West Germany, Early Germany, and Early Brazil are where VW produced the best quality parts and best fitting products.
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[mondshine]

The fuel gauge itself is actually thermally actuated.
Current flowing through the wire winding inside the gauge heats a small bi-metallic strip which deflects to move the needle.

The vibrator, by switching this current on and off, is sending an "average" of about 5V to the gauge. So between the reduced "average" voltage and the thermal actuation of the gauge needle, the gauge reading is stabilized to avoid radical movement from fuel sloshing in a partially filled tank.

Operating the gauge on straight 12-14 volts might work for a while, but you will probably burn up the gauge (if you haven't already).

The early water cooled VWs (Rabbits, Sciroccos) also used thermal fuel gauges, but they used a solid state DC buck converter chip instead of the gauge vibrator to reduce voltage to the gauge to 5VDC.

Why not just wire the gauge as it was intended???
If the gauge vibrator was not necessary, it would not have been installed when the car was built. Yes, you do need the vibrator.

[Das Ding]

Mondshine and Heimlich take a look at the image to double check my work.

Everything is wired back factory and appears to be working as designed.

It's a VW Thing miracle!!

Thank you both.

Das
[/img]

[mondshine]

I assume that the orange (on my monitor) wire is providing ignition power (Terminal 15).

I also assume that the pink wire is connected to the fuel sender.

If that is true, I would say that you are OK.

If you feel super ambitious, (while it's apart) get a load of this:

The buzzer can only sound when the engine is actually running and the belt breaks or you lose OP. This stuff was all from Amazon for <$20.

Good luck, Mondshine

[Das Ding]

Thank you Mondshine.
I saw this drawing elsewhere.
I would like to try it however I just want to get this car on the road!
Thank you again,
Das