I installed a 50A50-241 with a universal replacement part 50A55-843. All the connections were easy enough to transfer till I got to a white wire in slot E21 on the original Model. The replacement does not have a slot E21 and I am getting the following error message:
115 volt ac power reversed improper ground. Can anyone suggest what I need to fix this problem? Thanks

Here is a touble shoot procedure.

http://www.white-rodgers.com/wrdhom/pdfs/06_Cat_pages/Cat_06_pg0259_264.pdf

Pay attention to this note on page 1



A. Check continuity for C terminal on module to electrical service ground and
connection at the furnace junction box. If ground connection is open, check
module ground connection and the electrical service ground connection.
Repair and retest.
B. Re-connect electric power to system.
C. Check for voltage between the line neutral terminal and furnace ground. If
voltage exists, the main power supply lines are improperly connected to the
furnace (REVERSED POLARITY). Again disconnect electric power to system;
then reverse incoming supply leads to furnace. Repeat step.
D. Recheck system for proper operation.

See LINE and LINE N on page 4 here. Those are the leeds reversed. See below for this


http://www.white-rodgers.com/wrdhom/pdfs/instruction_sheets/0037-6265.pdf