How to resume trades is described under "Trading". Trades are stored in a .trd file in the Data folder, so they are not resumed when you delete that file.
There was a Z12.trd file in the directory, but I have only been running Z2 recently. I made a decision to copy this file to Z2.trd, and see what happens. I restarted 1.66.4, and the trades appear to be resumed.
