Hindsight, being 20/20. 18 volts and 6 amps is a lot of power to run a crane. Checking actual voltage probably done after meltdown.
I had a similiar problem. Where those output wires plug into the power board the socket failed. Most likely a poor connection. My 20/20 Hindsight is do not waste a Z-4000 throttle running lights at 16 volts and 8.5 amps. Normal parameters but time of use pushed it over the edge.