The manuals are correct, if you power them up in order, they automatically assemble into a stack. What the manual does not mention, is that the switches only do this if not in Ethernet stacking mode and they are now delivered with Ethernet stacking mode set by default. Once you switch that off and save/reboot, they self-assemble. I finally found a phone number to call and got help. Why the doc doesn't match the product is beyond me. The switches are not powered up now, or I'd look up the "magic" for this thread, but if memory serves, Clint Griffin (Dell) said to enable, configure, stack, stack-port stack, exit, exit, copy run start, restart. (or something very near that) for each switch.
I have 3 1548P switches. The top one is the master and is configured with and IP address. The next two are new (reboot after config delete startup-config). I have link cables connected 1:1-2:2, 2:1-3:2, 3:1-1:2. Using the RS-232 console on all three switches config show switch stack-ports show 1 and 2 Link Up, Admin status Disabled. The switches are routing VLAN 1 traffic, but all three think they are stack master. Only switch 1 has an IP configured, so whatever switch the Ethernet is attached to, ssh connects to switch 1. The manual says it will automatically join the stack if it has good link cabling, no Ethernet cabling and no saved config. This does not work.
How to configure a stack. (3 1548P)