fuel gauge

having a problem with my fuel gauge on my 2a, its got the series 3 dash and instruments, the fuel gauge only comes up to about a quater and i put in £30 worth of diesel the temp gauge only comes up about the same but it might need a thermostat, so please correct me if i am wrong, if i take the two wires off the tank sender and touch them together the gauge should go up to full if the gauge is ok, and this would then point to the sender being faulty or the voltage stableiser.

if you earth live lead to sender it should go to full on guage you often find if someones fitted new sender that they put it in so that arm gets trapped on its way up so never reads full

thats exactly what has happened, turned it 45 degrees and its fine, thanks JAMESMARTIN