Groucho,
There is no direct answer in the FCOM,if that is the sauce you are looking for....
However,the Engine start switch powers the EEC via the engine start lever in Idle or if the engine start switch in GND or CONT.(AMM wiring schematic 73-22-11).
The second part of the question is the link between no N1 info and subsequent loss of speed trim...i believe i answered it above and one needs to find the interaction between the EEC and the speed trim function.
The EEC gets info of N1 directly from the sensors or via the DEU,if no input then speed trim has no info to work with..(AMM 22-11).