"It sounds to me as though some wires are trapped under one of the mounting posts."
i suspect the same myself, but the lionel person i talked to was adamant that i would void the warranty by removing the shell. on the chance that it is something else, i declined to do that. so, i have to wait until august when the new repair facility will be overwhelmed.
"I am shocked nobody noted that the Older Legacy WP A-B-B-A F7s had smoke units in all of them."
i don't know about the F7's, but the TMCC F3's i had did not have smoke in the unpowered B, but it did have an operating coupler on the rear and, since it was a TMCC unit, the coupler could be operated when MU'ed with the powered A and B. the backup light would also illuminate in reverse. i actually miss those two features more than the smoke. i could run AB, but WP usually ran ABB on their section of the California Zephyr and, since it is my most prototypically correct train, i want to keep that configuration.