Rigged adapters so I could switch the nozzle heater and hotend thermistor at the board as suggested. Turned it on, no change in the readings. After watching for a minute or so to see if the nozzle temp would go down, I set the temp to about 50; as soon as I pressed the display button, got the MAXTEMP error. Tried a new nozzle heating element, it showed the error, both in the correct and reversed positions. Then used a new thermistor, cylindrical style, turned it on, and the temp showed normal!! (The wires at the 'bead' were bare.) Stopped there to reconnect wires and re-thread the thermistor the loom. I'll make a fresh start from scratch to do things properly later for a REAL check-out! Another thank you!
PS--Looking to the future. why didn't I check those in the first place, without having to involve you? Simple lack of experience and knowledge, I suppose....