This is the owners manual from archive.org (I haven't been able to find the service manual)
https://archive.org/details/Z180PCSeriesLaptopComputersOwnersManualZenithDataSystems1987
Here's the reassembly for my ZWL-183-92. I bet they're pretty similar.
From a (pretty) complete tear down, I would reassemble in the following order:
Mount board in case (parallel port, keyboard cable to board, mount board, mount keyboard, plug in keyboard, plug in modem, install modem cover)
Install drives (not pictured. Floppy data cable is much easier to install when the drives are removed. Note the 1 pin location on the floppy board, if the cable is reversed the drive may not work)
Install power distribution board (plug brightness/contrast, LCD power, LED/Speaker, mount with shield)
Attach power from distribution board (Floppy, hard drive card, power/charger board)
Install drive data and main power to board (FDD cable(s), IDE to HDD controller, HDD controller to board, power/charger board to main board)
LCD cable and power distro control(?) cable to board (you'll have to be folding the computer closed to get those)
Not mentioned: ground cables (black with ring terminals). These should essentially chain to connect all metal components/shields together. I didn't keep track of them very well, but I know there are the at least the following connection points: power distro shield, keyboard shield, floppy drive, HDD, screen hinge (center, this is where I hop from the top to the bottom), rear port fascia, parallel port fascia.
Hope this helps!
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