Stuck with a task in a LOGIC TESTS book. What "either of which" should mean?
If meaning of "either of which" is exclusive OR then solution is straightforward: B bears a true sign and all is clear.
I, though, incline to understand context much broader: from "none of the doors" to "both doors" can be wired. In this case task becomes more tedious to solve as one needs to write down boolean expressions for A and B signs and run them against two scenarios.
Part of the confusion is caused by the first part of the text where authors used "either of which..." and later in the paragraph they specifically used "one of the signs..."