The WT is nothing like the WP at all WP uses Curtis controller WP uses zapi. has it got electronic steering???? It does make a big difference to the codes. Fixed or folding platform????. The code I would look at first is the 304, check and clean the estop does the dash turn off when you isolate the truck as it has a micro switch on the bottom the fails all the time. Strip and clean the main switch they are prone to dirty contacts due to dust ingress finally is the battery good???? 304 is a power issue and a truck showing 304 will throw other codes as well.

Strange I don't have a listing for WT here in Canada -from what I see on the web the WT is very similar to WP but has stand on platform. Wiring is a common fault for brs/ors switch harness at base of steer tiller and the temp switch is very common. Don't be shy to cut off the ties and get a good look at all the flex points of the harness. Do you know what control system is in this Curtis or Sevcon?

I made a mistake , the forklift model is WT-3020.
Will the previous answer still apply?

Check that the brake switches are ok it's common on these to have cable breaks on them, also check the cables from the temperature sensor in the motor these break on the connectors. Finally check the motor encoder is good I've changed plenty of these too it's bolted into the end of the motor with an Allen bolt. Unlikely to be the motor we've nearly 50 Wp3020's on site and not changed a motor yet