Long shot here, but the older cars (A1's) had a voltage regulator chip on the back of the instrument cluster that regulated the voltage to all the gauge circuits so that they would indicate proper. I don't know if they still had it on the 90 jetta's but if it does and the chip is not regulating the voltage properly your gages would be off.
Otherwise you obviously could have a high resistance connection (rusted connector) between the sending unit and the gage.
a quick check of the sending unit position would be to remove the sending unit hook it up to the gauge and move it over its full range of movement to see if the gage ever goes to the full position. if it never indicates full then it is not the position of the detector
HTH Steve
Agh....
>
> Between the headliner dropping down and this friggen fuel gauge, this car is
> going to drive me nuts!
>
> Anyway, I replaced the fuel sending unit in the tank, thinking that it might
> correct the fuel gauge issue. However, after filling the tank full, the
> gauge still only reads to 3/4s of a tank. (Actually inbetween 3/4s and
> half). I am really lost as this problem is new, and never before was an
> issue...My nxt guess was that the gauge might be screwed up, or the sending
> unit in the tank is positioned wrong....does anybody have any wise ideas? >
> Thanks,
>
> Peter
>
> 1990 Jetta 1.8L Digifant
>
>
>