fuel gauge reading reversed!

[Cymru1]

i.e no key in the ignition and gauge reads quarter of a tank.
Put the ignition on and it drops to zero!

pulled most of the fuses and relays but still getting power from
some source. Only thing i can do at the moment to kill the power
is to disconnect the battery.

Fusebox seems dry but some slight corrosion on one of the earths.
All other electrics/dials seem perfect.

Anyone have an idea?

[willg54]

could this be the resistor thingy on the back of the cluster? on the back in the middle...little black thing with 3 legs. controls voltage to fuel guage and temp guarge IIRC