Always get another unit ! First check 500 amp fuse , it is main drive fuse I have seen a lot that check good under continuity but will not carry the voltage second you will have to remove battery and in battery tray there is a channel where the main cables lay over time batteries are leaking or have been over filled and acid gets on cables causing the rubber coating to expand and deteriorate and exposing the cable which can short out to frame
Also make sure they are in channel properly
If not battery will crush them
I retired from Clark dealer after 32 years
The worst case is you have a motor rebuilt or replace a controller either way much cheaper than new unit