as we know the fuel gauge not working is common on the z31,its usually a duff sender unit,my gauge has never worked,ive disconnected the sender unit in the boot and turned the ignition on and i get around 7.7 volts which suggests to me either a relay/circuit breaker is at fault......i had a similar problem on a front electric window reading about the same volts and it was the circuit breaker under the dash at fault........ ive checked all the relays/circuit breaker in the drivers footwell,and all the relays in the box on the drivers side under the bonnet,and its nothing to do with the 2 metal boxes by the tail lights in the drivers side wheelarch either,bit stumped at min,does anybody know the location of the relay that covers the fuel sender unit?the manual doesnt say anything